The catalytic performance of Ru–NHC alkylidene complexes: PCy₃ versus pyridine as the dissociating ligand

• Stefan Krehl,
• Diana Geißler,
• Sylvia Hauke,
• Oliver Kunz,
• Lucia Staude and
• Bernd Schmidt

Beilstein J. Org. Chem. 2010, 6, 1188–1198, doi:10.3762/bjoc.6.136

• reactions Allylic alcohol 8 [59] was chosen to test the catalysts investigated in this study for cross metathesis activity, because allylic alcohols are known to undergo undesired “redox isomerization” in the presence of Ru metathesis catalysts in some cases with the formation of ethyl ketones [47][60

• : 304.1683; Anal. calcd for C18H24O4: C, 71.0, H, 8.0, found: C, 70.8, H, 7.7. Cross-metathesis reactions General procedure: A solution of the allylic alcohol rac-8 (139 mg, 0.5 mmol) and the corresponding acrylate 9 (5 mmol) in dry and degassed toluene (1.0 mL for 0.5 mol·L–1, 5.0 mL for 0.1 mol·L–1) was

• metathesis reactions. Cross metathesis reactions with allylic alcohol 8. RCM of acrylate 3a. RCM reactions of acrylates to unsaturated lactones.a Ring closing enyne metathesis reactions catalyzed with E and H. Cross metathesis reactions catalyzed by D, E, and H. Supporting Information Supporting Information

Redox-active tetrathiafulvalene and dithiolene compounds derived from allylic 1,4-diol rearrangement products of disubstituted 1,3-dithiole derivatives

• Filipe Vilela,
• Peter J. Skabara,
• Christopher R. Mason,
• Thomas D. J. Westgate,
• Asun Luquin,
• Simon J. Coles and
• Michael B. Hursthouse

Beilstein J. Org. Chem. 2010, 6, 1002–1014, doi:10.3762/bjoc.6.113

• further change to the remnant allylic alcohol [10]; a related mechanism has been reported for a self-coupling intermolecular reaction, which involves an intermediate allylic cation generated under acidic conditions from an electron-rich thienylmethanol derivative, where no intramolecular rearrangement

Three step synthesis of single diastereoisomers of the vicinal trifluoro motif

• Vincent A. Brunet,
• Alexandra M. Z. Slawin and
• David O'Hagan

Beilstein J. Org. Chem. 2009, 5, No. 61, doi:10.3762/bjoc.5.61

• . Results and Discussion The chemistry was initiated from allylic alcohol 2 which can readily be prepared in enantiomerically pure form by hydrolytic kinetic resolution of vinyl epoxide 1 following Jacobsen’s protocol [13] (Scheme 3). Diol 2 was converted to tosyl ester 3 in a regioselective manner

• and relative stereochemistry of the crystalline threo-isomer (2R,3S,4S)-7a was confirmed by X-ray structure analysis as shown in Figure 2. With a strategy to access both stereoisomeric series of the allylic alcohol epoxides A in place, the fluorination reactions were then explored. The fluorination of

Acid- mediated reactions under microfluidic conditions: A new strategy for practical synthesis of biofunctional natural products

• Katsunori Tanaka and
• Koichi Fukase

Beilstein J. Org. Chem. 2009, 5, No. 40, doi:10.3762/bjoc.5.40

• required in a year with more than 98% purity. Namely, the preparation of 5 kg of pristane in about a week is necessary in order to supply enough material in the market. The challenging step in Scheme 1 is the acid-catalyzed dehydration of allylic alcohol 19. When the reaction was performed in 100 mg scale

• successful application of the microfluidic systems to the acid-mediated reactions during the N-glycan synthesis described above, we examined the microfluidic dehydration under the following conditions (Figure 3) [29]: Allylic alcohol 19 (1.0 M in THF) was mixed with a solution of p-TsOH (various

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

• gives rise to complex reaction mixtures due to the possibility of nitrene insertion. Cycloaddition of phenyl azide, however, to the unsaturated carbonyl 41 was readily accomplished to give triazoline 42 in 56% yield (Scheme 10) [53][54][55]. According to this scheme, the allylic alcohol 38 was oxidized

• leaving group X free for nucleophilic displacement with the nitrogen of the newly formed pyrroline. The synthesis began by Mitsunobu coupling of phenol 76 with allylic alcohol 77 to give ether 78, which was heated in N,N-dimethylaniline to trigger a Claisen rearrangement (Scheme 22). A sequence of

• D-ribose 193. Treatment of D-ribose in acetone with allylic alcohol in presence of catalytic amount of sulfuric acid provided the corresponding protected acetonide allyl glycoside. The primary alcohol was transformed into a N-Boc amine by successive Mitsunobu reaction, reduction and acylation to

Recent progress on the total synthesis of acetogenins from Annonaceae

• Nianguang Li,
• Zhihao Shi,
• Yuping Tang,
• Jianwei Chen and
• Xiang Li

Beilstein J. Org. Chem. 2008, 4, No. 48, doi:10.3762/bjoc.4.48

• (E)- or (Z)-allylic alcohol followed by Sharpless AE using (+)- or (−)-DET. This synthesis was quite flexible and all stereoisomers of the central THF core of solamin were easily obtained. The allyl alcohol 63 and the vinyl epoxide 66 were then coupled to construct the solamin skeleton 67. Subjecting

• iodoetherification of E-allylic alcohol 96, which was prepared from chiral alcohol 95a. The γ-lactone segment 99 was synthesized by α-alkylation of α-sulfenyl γ-lactone 15 with 98b. The carbon skeleton 100 was assembled in a convergent fashion from 97 and 99 through a Nozaki-Hiyama-Kishi reaction. Oxidation of 100

• efficient construction of the adjacent bis-THF backbone (Scheme 22). 1,5,9-Cyclododecatriene (86) was converted to the bis-allylic alcohol 154 through selective oxidation and Wittig extension followed by DIBAL-H reduction. The stereogenic centres in the bis-THF backbone 156 were then installed by sequential

Sordarin, an antifungal agent with a unique mode of action

• Huan Liang

Beilstein J. Org. Chem. 2008, 4, No. 31, doi:10.3762/bjoc.4.31

• 25 was obtained through another cuprate addition, followed by NaBH4 reduction of the ketone and subsequent deoxygenation under Barton-McCombie conditions. Exchange of the MOM for a TBS protecting group and treatment with mCPBA furnished an epoxide, which was converted into allylic alcohol 26 by

• , formation of an enol triflate using phenyl triflimide and installation of the isopropyl group by an addition-elimination sequence using a thienylcuprate reagent. Removal of the MOM groups and selective oxidation of the allylic alcohol by MnO2 led to the cycloaddition substrate 33, heating of which at 40 °C

• ). Selective cleavage of the TBS group and PCC oxidation surrendered ketone 49. Diastereoselective addition of vinylmagnesium chloride and exchange of the enol protecting group gave allylic alcohol 50. The substrate 51 for the Tsuji-Trost reaction was prepared by carbethoxylation of the allylic alcohol and

An efficient synthesis of tetramic acid derivatives with extended conjugation from L-Ascorbic Acid

• Biswajit K. Singh,
• Surendra S. Bisht and
• Rama P. Tripathi

Beilstein J. Org. Chem. 2006, 2, No. 24, doi:10.1186/1860-5397-2-24

• studies. In such an earlier study, [37] with BuLi at -78°C used as the base for the Wittig olefination, lower yields and poor stereoselection was observed as compared to our uncatalysed ambient temperature reaction where ZZ isomers were predominantly formed. The Z configuration of the allylic alcohol was

Synthesis of 2,6-trans- disubstituted 5,6-dihydropyrans from (Z)-1,5-syn-endiols

• Eric M. Flamme and
• William R. Roush

Beilstein J. Org. Chem. 2005, 1, No. 7, doi:10.1186/1860-5397-1-7

• silylation of the allylic alcohol unit followed by mesylate formation and base-promoted nucleophilic displacement. Findings We recently reported a one-pot double allylboration reaction sequence which provides (Z)-1,5-syn-endiols from simple aldehyde starting materials with excellent diastereo- and

• hydroxyl groups. Selective activation of the allylic alcohol in 2 as a leaving group followed by nucleophilic attack by the homoallylic alcohol will lead to dihydropyran 3. However, activation of the homoallylic alcohol followed by nucleophilic attack by the allylic alcohol will provide the enantiomeric

• allylic alcohol to be displaced in this intramolecular substitution process, the allylic C-O bond substantially deviates from coplanarity with the adjacent π-system. Therefore, the difference in relative rates of displacement of the two activated hydroxyl groups is much less than originally anticipated

Mixtures of monodentate P-ligands as a means to control the diastereoselectivity in Rh-catalyzed hydrogenation of chiral alkenes

• Manfred T. Reetz and
• Hongchao Guo

Beilstein J. Org. Chem. 2005, 1, No. 3, doi:10.1186/1860-5397-1-3

• regioselectivity of transition metal catalyzed processes has been extended to include diastereoselectivity. Accordingly, 1,2- and 1,3-asymmetric induction in the Rh-catalyzed hydrogenation of a chiral allylic alcohol and a chiral homo-allylic alcohol has been studied by using mixtures of monodentate P-ligands. It

• extensive manner. For example, Brown reported the Rh-catalyzed hydrogenation of the racemic allylic alcohol 1 with formation of diastereomers 2 and 3, ketone 4 forming as a side product due to undesired isomerization.[29] From a small collection of mono-phosphines and bidentate diphosphines, diphos-4 led to

• analogous Rh-catalyzed hydrogenation of the homo-allylic alcohol 5 with formation of diastereomers 6 and 7 was considered. Here again one enantiomeric form is shown arbitrarily, although a racemate was used. Monodentate P-ligands P1 – P23 were employed in the hydrogenation reactions, the Rh:ligand ratio

Methods for the synthesis of polyhydroxylated piperidines by diastereoselective dihydroxylation: Exploitation in the two-directional synthesis of aza-C-linked disaccharide derivatives

• Andrew Kennedy,
• Adam Nelson and
• Alexis Perry

Beilstein J. Org. Chem. 2005, 1, No. 2, doi:10.1186/1860-5397-1-2

• from oxidation to the corresponding α,β-unsaturated ketone,[47] followed by conjugate addition. The dihydroxyation of the anti allylic alcohol 19 under Upjohn conditions was not synthetically useful (entry 8a, Table 1). Although dihydroxyation of the remote allyl group was rapid, the dihydroxylation of

• 2a with 2b, Table 1). With the syn allylic alcohol 17, dihydroxylation was highly (>95:<5) syn selective, yielding the triacetate 20B in 70% yield after peracetylation (entry 1b, Table 1). We have previously observed that the pseudo-equatorial allylic hydroxyl groups of similar dihydropyrans had been

• the anti allylic alcohol 19 was predominantly directed by the hydroxyl group, and the products 22C and 22D were obtained in 26% and 8% yield respectively after a rather sluggish acetylation reaction (entry 8b, Table 1). Here, with the butyl and p-toluenesulfonyl groups in pseudoaxial positions,[40