Olefin metathesis catalysts embedded in β-barrel proteins: creating artificial metalloproteins for olefin metathesis

• Daniel F. Sauer,
• Johannes Schiffels,
• Takashi Hayashi,
• Ulrich Schwaneberg and
• Jun Okuda

Beilstein J. Org. Chem. 2018, 14, 2861–2871, doi:10.3762/bjoc.14.265

• . These transformations include all three fundamental olefin metathesis reactions: ring-opening metathesis polymerization (ROMP), ring-closing metathesis (RCM) as well as cross metathesis (CM) (Scheme 2). Review Artificial metatheases – anchoring approaches Metalloproteins that contain one or more metal

• Chauvin [2]. Right: Potential influence of the protein as second coordination sphere in the transition state that lead to different metathesis products. (i) Ring-opening metathesis polymerization (ROMP), (ii) ring-closing metathesis (RCM) and (iii) cross metathesis (CM). Biotinylated GH-type catalysts for

Synthesis of a tyrosinase inhibitor by consecutive ethenolysis and cross-metathesis of crude cashew nutshell liquid

• Jacqueline Pollini,
• Valentina Bragoni and
• Lukas J. Gooßen

Beilstein J. Org. Chem. 2018, 14, 2737–2744, doi:10.3762/bjoc.14.252

• of the entire mixture and subsequent selective precipitation of 6-(ω-nonenyl)salicylic acid from cold pentane. The olefinic side chain of this intermediate was elongated by its cross-metathesis with 1-hexene using a first generation Hoveyda–Grubbs catalyst, which was reused as precatalyst in a

• subsequent hydrogenation step. Overall, the target compound was obtained in an overall yield of 61% based on the unsaturated anacardic acid content and 34% based on the crude CNSL. Keywords: cashew nutshell liquid; cross-metathesis; renewable feedstock; sustainable chemistry; tyrosinase inhibitor

• of the anacardic acid component of CNSL presents several challenges. Since CNSL consists of a mixture of acids, phenols and resorcins with saturated and unsaturated side chains, it seemed to be impossible to derive a single product with a shorter side chain via a cross-metathesis with a short olefin

Domino ring-opening–ring-closing enyne metathesis vs enyne metathesis of norbornene derivatives with alkynyl side chains. Construction of condensed polycarbocycles

• Ritabrata Datta and
• Subrata Ghosh

Beilstein J. Org. Chem. 2018, 14, 2708–2714, doi:10.3762/bjoc.14.248

• structure of the Diels–Alder adduct is 14. The formation of triene 11 could be attributed to cross metathesis of the ruthenium alkylidene 8a with ethylene. No product arising out of ROM of norbornene derivative 7a was formed. It is worth mentioning that Spandl et al. [43] reported the metathesis of

• acetate 17 also remained inert when subjected to metathesis conditions with G-I as well as with G-II. Neither ring opening of the norbornene nucleus nor cross metathesis of the alkyne with ethylene did occur. To have an understanding about the inertness of 17 towards metathesis we decided to prepare the

• ) which prohibits intramolecular addition of the ruthenium alkylidine to form ruthena cyclobutane 22. The alkylidine 21 then undergoes cross metathesis with ethylene to form the product 11. The ruthenium alkylidine 8b possibly fails to form chelate 21 (R = Ac) due to the electron deficient nature of the

Ring-opening metathesis of some strained bicyclic systems; stereocontrolled access to diolefinated saturated heterocycles with multiple stereogenic centers

• Zsanett Benke,
• Melinda Nonn,
• Márton Kardos,
• Santos Fustero and
• Loránd Kiss

Beilstein J. Org. Chem. 2018, 14, 2698–2707, doi:10.3762/bjoc.14.247

• multiple stereogenic centers thus synthesized can be considered interesting scaffolds for further transformations in view of the access of novel three-dimensional functionalized scaffolds through cross-metathesis (CM). An illustrative example is shown on Scheme 7. Divinylated γ-lactam (±)-19 selected as a

• and, therefore, the vinyl group closest to the ring N-atom becomes more reactive in cross-metathesis (Figure 2). Similar chemodiscriminations of C–C double bonds were previously observed in the transformation of various alkenylated lactams or amino esters [16]. Lactams are known to be useful

• of an ethylene atmosphere for the time indicated in the text (monitored by TLC). After completion of the reaction, the mixture was concentrated under vacuum and purified by column chromatography on silica gel (n-hexane/EtOAc). General procedure for cross-metathesis To a solution of γ-lactam

Synergistic approach to polycycles through Suzuki–Miyaura cross coupling and metathesis as key steps

• Sambasivarao Kotha,
• Milind Meshram and
• Chandravathi Chakkapalli

Beilstein J. Org. Chem. 2018, 14, 2468–2481, doi:10.3762/bjoc.14.223

• Diels–Alder reaction, Claisen rearrangement, cross-metathesis, and cross-enyne metathesis are used. The synergistic combination of these powerful reactions is found to be useful for the construction of complex targets and fulfill synthetic brevity. Keywords: Claisen rearrangement; Diels–Alder reaction

• reaction occurs under mild reaction conditions. Among different metathetic processes, ring-closing metathesis (RCM) [1][2][3][4][5][6] is of a greater interest than cross-metathesis (CM). It is a widely used protocol for the synthesis of unsaturated cyclic systems [7]. Palladium-catalyzed Suzuki–Miyaura

Efficient catalytic alkyne metathesis with a fluoroalkoxy-supported ditungsten(III) complex

• Henrike Ehrhorn,
• Janin Schlösser,
• Dirk Bockfeld and
• Matthias Tamm

Beilstein J. Org. Chem. 2018, 14, 2425–2434, doi:10.3762/bjoc.14.220

• cleaving the W≡W bond in W2F3 with 1-phenyl-1-propyne. The catalytic alkyne metathesis activity of these metal complexes was determined in the self-metathesis, ring-closing alkyne metathesis and cross-metathesis of internal and terminal alkynes, revealing an almost equally high metathesis activity for the

• ]. The catalyst III, which is capable of promoting conventional alkyne metathesis [19], also proved to be highly active in the cross metathesis of symmetric 1,3-butadiynes to form unsymmetrically substituted 1,3-butadiynes [30]. W. Zhang and his group introduced several multidentate phenoxide ligands to

• ditungsten catalyst W2F3 was also employed in alkyne cross-metathesis (ACM), a reaction which is of large interest for the application of alkyne metathesis, but often leads to product mixtures. Therefore, (trimethylsilyl)propyne and (trimethylsilyl)acetylene were chosen as reaction partners in ACM, since

Studies towards the synthesis of hyperireflexolide A

• G. Hari Mangeswara Rao

Beilstein J. Org. Chem. 2018, 14, 2106–2111, doi:10.3762/bjoc.14.185

• cyclopentane 5, a functionalized key intermediate, is presented. Compound 5 is involved in hydrolysis, α-allylation at C-8 and α-methylation at C-10 stereoselectively from the convex face. Then it is subjected to cross metathesis to give α,β-unsaturated ketone 11 as precursor in the total synthesis of

• hyperireflexolide A. Keywords: alkylation; allylation; cross metathesis; hyperireflexolide A; spiroterpene; Introduction Hyperireflexolide A (1) [1] is a spiroterpenoid, isolated from hypericum reflexum, plants of the genus hypericum (Figure 1). Hyperireflexolide A is widely used in folk medicine, displays

• with 2-bromopropene followed by lactonization. Enone 3 could be synthesized from 4 by installation of the methyl group at C-10 followed by cross metathesis reaction. Compound 4 could be obtained from the γ-lactone-fused cyclopentane 5 by deprotection of C-9 followed by allylation at C-8. Previously, we

Aminosugar-based immunomodulator lipid A: synthetic approaches

• Alla Zamyatina

Beilstein J. Org. Chem. 2018, 14, 25–53, doi:10.3762/bjoc.14.3

• -hexadecanoyloxy-15-methylhexadecanoic acids an efficient cross-metathesis has been employed [98]. Reduction of the 2-azido group with Zn in acetic acid, followed by acylation with the respective 3-O-benzyl protected fatty acid provided the key intermediate 45. Sequential protecting group manipulation (3’-O-Lev, 3

Synthesis and supramolecular properties of regioisomers of mononaphthylallyl derivatives of γ-cyclodextrin

• Markéta Bláhová,
• Sergey K. Filippov,
• Lubomír Kováčik,
• Jiří Horský,
• Simona Hybelbauerová,
• Zdenka Syrová,
• Tomáš Křížek and
• Jindřich Jindřich

Beilstein J. Org. Chem. 2017, 13, 2509–2520, doi:10.3762/bjoc.13.248

• a cross-metathesis between previously described regioisomers of mono-O-allyl derivatives of γ-CD and 2-vinylnaphthalene which gives yields of about 16–25% (2–5% starting from γ-CD). To increase the overall yields, we have developed another method, based on a direct alkylation of γ-CD with 3

• light scattering (DLS) [18][19][20][21] and cryo-transmission electron microscopy (Cryo-TEM) [22][23][24]. Results and Discussion Synthesis We present two approaches for the synthesis of naphthylallyl (NA) derivatives. The first approach is a cross-metathesis of peracetylated allyl derivatives of γ-CD

• based on a direct alkylation of γ-CD with 2-(3-chloroprop-1-enyl)naphthalene. Cross-metathesis Mono 2I-O-, 3I-O- and 6I-O-naphthylallyl-γ-CDs (2-O-NA-γ-CD, 2a, 3-O-NA-γ-CD, 2b, 6-O-NA-γ-CD, 2c) were prepared from peracetylated O-allyl derivatives [14] by cross-metathesis with 2-vinylnaphthalene (Scheme

Homologated amino acids with three vicinal fluorines positioned along the backbone: development of a stereoselective synthesis

• Raju Cheerlavancha,
• Ahmed Ahmed,
• Yun Cheuk Leung,
• Aggie Lawer,
• Qing-Quan Liu,
• Marina Cagnes,
• Hee-Chan Jang,
• Xiang-Guo Hu and
• Luke Hunter

Beilstein J. Org. Chem. 2017, 13, 2316–2325, doi:10.3762/bjoc.13.228

• fluoride, then deoxyfluorination). We therefore sought to apply O’Hagan’s method to the target 6b (Scheme 3, boxed). Accordingly, the enantiopure allylic alcohol 27 [35] was extended through a cross-metathesis reaction to deliver the disubstituted alkene 30 (Scheme 3). Compound 30 became the substrate for

• 27 (Scheme 3). Compound 35 was carried through the same set of reactions that were described previously for substrate 27 (Scheme 3). Thus, 35 underwent a cross metathesis reaction to furnish 36 in good yield (Scheme 4). Compound 36 then became the substrate for a Sharpless asymmetric epoxidation

Synthesis of 2-aminosuberic acid derivatives as components of some histone deacetylase inhibiting cyclic tetrapeptides

• Shital Kumar Chattopadhyay,
• Suman Sil and
• Jyoti Prasad Mukherjee

Beilstein J. Org. Chem. 2017, 13, 2153–2156, doi:10.3762/bjoc.13.214

• the alternate preparation of (S)-2-aminohept-6-enoate ester as a building block and its diversification through a cross-metathesis reaction to prepare the title compounds. The utility of the protocol is demonstrated through the preparation of three suberic acid derivatives of relevance to the design

• and the synthesis of peptides of biological relevance. Keywords: α-amino acid; catalysis; chiral pool; cross metathesis; cyclic peptides; Introduction α-Aminosuberic acid (Asu) is a component of apicidin F (1, Figure 1) belonging to an interesting class of cyclic tetrapeptides displaying

• of 27% over seven high yielding simple steps. Having access to the building block 11, we focused on its conversion to the targeted Asu derivatives through cross metathesis (CM) [20] with conjugated olefins 13a–d (Scheme 2). In recent years, the cross-metathesis reaction has emerged as a valuable tool

High-speed vibration-milling-promoted synthesis of symmetrical frameworks containing two or three pyrrole units

• Marco Leonardi,
• Mercedes Villacampa and
• J. Carlos Menéndez

Beilstein J. Org. Chem. 2017, 13, 1957–1962, doi:10.3762/bjoc.13.190

• achieved by a different approach involving the homodimerization of 1-allyl- or 1-homoallylpyrroles by application of cross-metathesis chemistry. Keywords: diversity-oriented synthesis; mechanochemistry; multicomponent reactions; pyrroles; solvent-free synthesis; Introduction Symmetrical molecules formed

• fragments, we briefly examined the homodimerization reactions of 2-allyl- and 2-homoallylpyrroles via cross-metathesis, which should give access to spacers not easily accessible by the previously described route. The starting materials for this study (compounds 11) were readily prepared under the conditions

• a double bond in their spacer chain were obtained by a different approach involving the homodimerization of 1-allyl- or 1-homoallylpyrroles by cross-metathesis. Scope of the synthesis of symmetrical bispyrrole derivatives. Our synthetic planning and structural diversity of starting materials

Mechanochemical synthesis of small organic molecules

• Tapas Kumar Achar,
• Anima Bose and
• Prasenjit Mal

Beilstein J. Org. Chem. 2017, 13, 1907–1931, doi:10.3762/bjoc.13.186

• . Importantly catalytic application of these mechano-synthesized complexes are also explored. Friščić and co-workers recently reported an efficient mechanochemical approach towards Ru-based Hoveyda–Grubbs catalyzed olefin metathesis, cross-metathesis and ring-closing metathesis reactions (Scheme 49) [181

The chemistry and biology of mycolactones

• Matthias Gehringer and
• Karl-Heinz Altmann

Beilstein J. Org. Chem. 2017, 13, 1596–1660, doi:10.3762/bjoc.13.159

Modular synthesis of the pyrimidine core of the manzacidins by divergent Tsuji–Trost coupling

• Sebastian Bretzke,
• Stephan Scheeff,
• Felicitas Vollmeyer,
• Friederike Eberhagen,
• Frank Rominger and
• Dirk Menche

Beilstein J. Org. Chem. 2016, 12, 1111–1121, doi:10.3762/bjoc.12.107

• -metathesis of a challenging homoallylic urea substrate, which proceeds in good yields in the presence of an organic phosphoric acid. Keywords: cross-metathesis; natural products; pyrimidines; Tsuji–Trost reaction; synthetic methods; Introduction Chiral pyrimidine motifs constitute prevalent structural

• substrate 14 was prepared from amine 12 by cross-metathesis with 2-butene-1,4-diol (13) in the presence of Grubbs-II catalyst 21. However, in the subsequent coupling reactions of 14 with TsNCO it became apparent that this homoallylic amine was too unreactive to enable a double addition to access 15 directly

• . Therefore, a stepwise approach towards 19 was pursued instead. This involved either a coupling of 12 first with isocyanate to give 16 followed by a cross-metathesis or starting with the cross-metathesis to 18 and subsequent installment of the urea motif. As shown in the table inserted in Scheme 3 for

A cross-metathesis approach to novel pantothenamide derivatives

• Jinming Guan,
• Matthew Hachey,
• Lekha Puri,
• Vanessa Howieson,
• Kevin J. Saliba and
• Karine Auclair

Beilstein J. Org. Chem. 2016, 12, 963–968, doi:10.3762/bjoc.12.95

• larger groups via cross-metathesis. The method was applied in the synthesis of a new pantothenamide with improved stability in human blood. Keywords: antibiotic; antiplasmodial; coenzyme A; metathesis; pantothenate; Introduction Bacteria, fungi, and parasites are all rapidly acquiring resistance to

• at the geminal dimethyl group. This route takes advantage of the reported path to 2 combined with cross-metathesis. Results and Discussion Establishing the synthetic route Based on the success of the synthetic route published by Akinnusi et al. [18] to generate derivatives modified at the geminal

• dimethyl moiety of pantothenamides, it was envisaged that allyl derivatives, such as 2 or its precursors, could be good starting points to add larger moieties via cross-metathesis [19]. Two cross-metathesis catalysts were used here (Figure 2): Grubbs’ 2nd generation catalyst (3) and the more versatile

Effective immobilisation of a metathesis catalyst bearing an ammonium-tagged NHC ligand on various solid supports

• Krzysztof Skowerski,
• Jacek Białecki,
• Stefan J. Czarnocki,
• Karolina Żukowska and
• Karol Grela

Beilstein J. Org. Chem. 2016, 12, 5–15, doi:10.3762/bjoc.12.2

• . Model metathesis reactions used in tests. Supported catalyst 8 in sequential cross metathesis and reduction. Results of olefin metathesis conducted in AcOEt.a Results of olefin metathesis conducted in toluene, 80 °C. Supporting Information Supporting Information File 68: Experimental procedures and

• along with the ruthenium content in crude metathesis products is summarised in Table 2. The products of RCM and ene–yne metathesis were obtained with good to excellent yields with the use of 0.1–0.5 mol % of catalyst. Functionalised olefins 19 and 21 were isolated with excellent yield after cross

• metathesis (CM) reactions run with only 1 mol % of catalyst. Importantly, the residual ruthenium content in the crude products was very low (determined by ICP-MS method). Reaction work-up was performed solely by filtration of the reaction mixture through a piece of cotton and evaporation of the volatiles, to

New metathesis catalyst bearing chromanyl moieties at the N-heterocyclic carbene ligand

• Agnieszka Hryniewicka,
• Szymon Suchodolski,
• Agnieszka Wojtkielewicz,
• Jacek W. Morzycki and
• Stanisław Witkowski

Beilstein J. Org. Chem. 2015, 11, 2795–2804, doi:10.3762/bjoc.11.300

• modified stereoselective catalysts were described [5][6][7][8]. Over the last few years, considerable attention has also been paid to immobilisation and tagging of catalysts and especially on making them more environmentally friendly [9][10][11][12][13][14]. Alkene cross-metathesis (CM) is a convenient

• -hydroxychroman and –NH2 in 6-aminochroman). Testing of the new catalyst The catalyst proved very active in model cross-metathesis reactions, especially with olefins containing electron-withdrawing groups. For example the reaction of allylbenzene and ethyl acrylate at room temperature was almost quantitative

Diversity-oriented synthesis of analogues of the novel macrocyclic peptide FR-225497 through late stage functionalization

• Jyotiprasad Mukherjee,
• Suman Sil and
• Shital Kumar Chattopadhyay

Beilstein J. Org. Chem. 2015, 11, 2487–2492, doi:10.3762/bjoc.11.270

• which involves a late-stage functionalization of a macrocyclic scaffold through cross metathesis in an attempt to create diversity. The utility of this protocol is demonstrated through the preparation of three structural analogues of the important naturally occurring histone deacetylase inhibitor FR

• -225497. Keywords: cross metathesis; cyclic peptides; diversity oriented synthesis; macrocycle; Introduction Diversity-oriented synthesis (DOS) has been established as an important paradigm in drug discovery [1][2][3][4][5][6][7]. Although the major focus is on the synthesis of small molecular libraries

• differ in their end groups. Although there are excellent synthetic approaches to nearly all of such known targets [15], the development of a simple diversity-oriented approach suitable for modification of the compounds remains desirable. Results and Discussion We thought that a cross metathesis reaction

Beyond catalyst deactivation: cross-metathesis involving olefins containing N-heteroaromatics

• Kevin Lafaye,
• Cyril Bosset,
• Lionel Nicolas,
• Amandine Guérinot and
• Janine Cossy

Beilstein J. Org. Chem. 2015, 11, 2223–2241, doi:10.3762/bjoc.11.241

• Alkenes containing N-heteroaromatics are known to be poor partners in cross-metathesis reactions, probably due to catalyst deactivation caused by the presence of a nitrogen atom. However, some examples of ring-closing and cross-metathesis involving alkenes that incorporate N-heteroaromatics can be found

• delineate some guidelines for the use of these challenging substrates in metathesis reactions. Keywords: catalyst deactivation; cross-metathesis; N-heteroaromatic; pyridine; ring-closing metathesis; Introduction Over the past decades, metathesis has become a key reaction within the organic chemist’s

• allow the use of primary and secondary amines in ring-closing metathesis (RCM) and cross-metathesis (CM), and one of them is the transformation of amines into carbamates, amides or sulfonamides [27][28][29]. As an alternative, metathesis reactions can be performed with olefins possessing ammonium salts

Computational study of productive and non-productive cycles in fluoroalkene metathesis

• Markéta Rybáčková,
• Jan Hošek,
• Ondřej Šimůnek,
• Viola Kolaříková and
• Jaroslav Kvíčala

Beilstein J. Org. Chem. 2015, 11, 2150–2157, doi:10.3762/bjoc.11.232

• catalytic cycle proceeding through a ruthenacyclobutane intermediate bearing fluorines in positions 2 and 4. Moreover, the calculations showed that the cross-metathesis of perfluoro- or perhaloalkenes should be a feasible process and that the metathesis is not very sensitive to stereochemical issues

• alkenes to hydrofluoroalkenes. Moreover, just recently a successful cross metathesis of perfluoroalkenes with vinyl ethers has been published [35]. The reported computations dealing with the metathesis of fluoroalkenes are also extremely scarce. Thus, the mechanism of the cross metathesis of norbornene

Ru complexes of Hoveyda–Grubbs type immobilized on lamellar zeolites: activity in olefin metathesis reactions

• Hynek Balcar,
• Naděžda Žilková,
• Martin Kubů,
• Michal Mazur,
• Zdeněk Bastl and
• Jiří Čejka

Beilstein J. Org. Chem. 2015, 11, 2087–2096, doi:10.3762/bjoc.11.225

• of 1,7-octadiene and (−)-β-citronellene; HGIIN+Cl− on SBA-15 (HGIIN+Cl−/SBA-15) was the most active (TON up to 16000 in RCM of citronellene). HGIIN+Cl−/SBA-15 proved its versatility in RCM, enyne metathesis, metathesis of methyl oleate, and cross-metathesis of electron deficient methyl acrylate with

• -trifluoroacetamide (DAF), and (ii) in self-metathesis and cross-metathesis of methyl oleate. Lamellar (two dimensional) zeolites represent a subgroup of zeolitic materials, in which one of the dimension of the crystals is usually limited to 2–3 nm and is around one unit cell [24][25]. Depending on the structure of

• . The cumulative TON achieved in 7 runs was 1491. The results evidence very firm attachment of catalytically active species to the surface of zeolites and their good stability. Catalyst activity in self-metathesis and cross-metathesis of methyl oleate Conversion curves for self-metathesis of methyl

Olefin metathesis in air

• Lorenzo Piola,
• Fady Nahra and
• Steven P. Nolan

Beilstein J. Org. Chem. 2015, 11, 2038–2056, doi:10.3762/bjoc.11.221

• reactions of tri- and tetrasubstituted olefins [42][46], cross-metathesis (CM) to afford trisubstituted olefins [44] and CM and RCM reactions of electron-withdrawing substituted olefins [45]. In comparison to the 1st generation, they show a generally higher stability towards thermal degradation [41][42][43

• retained the properties of stability and recyclability. In 2002, Hoveyda et al. reported the Hoveyda–Grubbs’ 2nd generation type catalyst 36 (Figure 3) [56]: Complex 36, bearing an unsymmetrical and chiral NHC, was active in the asymmetric ring-opening cross-metathesis (RO/CM) in air using undistilled

New aryloxybenzylidene ruthenium chelates – synthesis, reactivity and catalytic performance in ROMP

• Patrycja Żak,
• Szymon Rogalski,
• Mariusz Majchrzak,
• Maciej Kubicki and
• Cezary Pietraszuk

Beilstein J. Org. Chem. 2015, 11, 1910–1916, doi:10.3762/bjoc.11.206

• have also been independently studied by Skowerski and Grela [10]. Phenoxybenzylidene complexes have been demonstrated to behave like latent catalysts in common testing reactions involving ring opening metathesis polymerisation (ROMP) of COD, norbornene derivative and dicyclopentadiene as well as cross

• metathesis (CM) of allylbenzene with Z-1,4-(diacetoxy)but-2-ene [9][10]. Although catalysts 1a–d are characterized by a number of advantages, they are not free from some weaknesses. They showed in some reactions a non-negligible catalytic activity in the absence of activators [9][10] and an instability of

Stereochemistry of ring-opening/cross metathesis reactions of exo- and endo-7-oxabicyclo[2.2.1]hept-5-ene-2-carbonitriles with allyl alcohol and allyl acetate

• Piotr Wałejko,
• Michał Dąbrowski,
• Lech Szczepaniak,
• Jacek W. Morzycki and
• Stanisław Witkowski

Beilstein J. Org. Chem. 2015, 11, 1893–1901, doi:10.3762/bjoc.11.204

• -oxanorbornene) followed by cross metathesis with a cross partner (e.g., propene) to give the respective ring-opening cross metathesis (ROCM) products. Preliminary analysis suggested that these transformations lead mainly to incorporation of two molecules of a coupling partner, if present in excess, into

• chromatograms recorded from crude reaction mixtures described in Table 1: a) entry 1 and b) entry 5. Numbering of carbon atoms in cross metathesis products. ROCM reactions of 7-oxanorbornene. Metathesis products of exo- and endo-7-oxabicyclo[2.2.1]hept-5-en-2-carbonitriles (1 and 2) with allyl acetate (3) or