Highly substituted benzannulated cyclooctanol derivatives by samarium diiodide-induced cyclizations

• Jakub Saadi,
• Irene Brüdgam and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2010, 6, 1229–1245, doi:10.3762/bjoc.6.141

• to the position of the methoxycarbonyl group and the hydroxyl group. In general, cis-configured products directly undergo a subsequent cyclization to the corresponding γ-lactones. It is noteworthy that the additionally introduced stereogenic centre bearing the methyl group is also generated

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

• ). Toluene was preferred over dichloromethane, because reactions are more conveniently conducted at elevated temperatures in this solvent. The acrylates 3 investigated in ring closing metathesis reactions with catalysts D, E and H are listed in Figure 5, together with the resulting unsaturated lactones 4

• . Results for the ring closing metathesis of acrylates 3a–g are summarized in Table 2. Lactones 4b–f [50] are accessible in preparatively useful yields with catalyst loadings of 2.5 mol % to 5.0 mol % if catalysts D and E are used. Conversions observed with catalyst H under otherwise identical conditions

• chromatography on silica to give the corresponding lactones 4. The ratio of lactone 4 to acrylate 3 was determined by integration of characteristic, baseline separated signals in the 1H NMR-spectrum of the crude reaction mixture. Representative example: 5-phenylfuran-2(5H)-one (4f). This compound was obtained as

Tandem catalysis of ring-closing metathesis/atom transfer radical reactions with homobimetallic ruthenium–arene complexes

• Yannick Borguet,
• Xavier Sauvage,
• Guillermo Zaragoza,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2010, 6, 1167–1173, doi:10.3762/bjoc.6.133

• generate active species in situ. The two catalytic processes were first carried out independently in a case study before the whole sequence was optimized and applied to the synthesis of several polyhalogenated bicyclic γ-lactams and lactones from α,ω-diene substrates bearing trihaloacetamide or

• reactions with homobimetallic ruthenium–indenylidene complex 1 to generate active species in situ. The two catalytic processes were first carried out independently in a case study before the whole sequence was optimized and applied to the synthesis of several polyhalogenated bicyclic γ-lactams and lactones

Systematic investigations on the reduction of 4-aryl-4-oxoesters to 1-aryl-1,4-butanediols with methanolic sodium borohydride

• Subrata Kumar Chaudhuri,
• Manabendra Saha,
• Amit Saha and
• Sanjay Bhar

Beilstein J. Org. Chem. 2010, 6, 748–755, doi:10.3762/bjoc.6.94

• the keto moiety. Results of a detailed and systematic investigation of the reaction are described. Keywords: diols; esters; lactones; reduction; Introduction Chemoselective reductions of aldehydes, ketones and imines are generally accomplished using NaBH4 in methanol where other reducible functional

• observed that the reduction of the keto group in the γ-oxoesters 1a and 3 (entries 1 and 2 in Table 3) with the formation of the lactones 9 and 4 as one of the products was much faster than the reduction of aryl alkyl ketones (entries 3 and 4 in Table 3). Therefore, formation of lactone as the intermediate

• corresponding saturated 1,4-butanediols has been firmly established. However, the reason for more facile reduction of the γ-aryl-lactones to diols and the relative reluctance of the γ-alkyl analogues is not yet clear. Conclusion From the above study, a novel method utilizing NaBH4 in methanol that can provide

Synthesis of gem-difluoromethylenated analogues of boronolide

• Jing Lin,
• Xiao-Long Qiu and
• Feng-Ling Qing

Beilstein J. Org. Chem. 2010, 6, No. 37, doi:10.3762/bjoc.6.37

• aldehyde 9 with the fluorine-containing building block 11 and the efficient construction of α,β-unsaturated-δ-lactones 15a–b via BAIB/TEMPO-procedure. Keywords: boronolide; gem-difluoromethylenated analogues; gem-difluoropropargylation; α,β-unsaturated-δ-lactones; Introduction (+)-Boronolide (1

• and the efficient construction of α,β-unsaturated-δ-lactones 15a–b via the BAIB/TEMPO-procedure. Boronolide (1), boronolide analogues 2–3 and gem-difluoromethylenated analogues 4–7. Retrosynthetic analysis of target molecules 4–7. Synthesis of target molecules 4–5. Synthesis of target molecules 6–7

2-Phenyl- tetrahydropyrimidine- 4(1H)-ones – cyclic benzaldehyde aminals as precursors for functionalised β²-amino acids

• Markus Nahrwold,
• Arvydas Stončius,
• Anna Penner,
• Beate Neumann,
• Hans-Georg Stammler and
• Norbert Sewald

Beilstein J. Org. Chem. 2009, 5, No. 43, doi:10.3762/bjoc.5.43

• ten minutes at 0 °C – virtually without formation of by-products. A similar procedure has formerly been employed by Bella et al. for the reduction of α-halogenated, α,β-unsaturated lactones [47]. The racemic fully protected heterocycle rac-5 as well as the enantiopure compound (S)-5 derived from (R)-4

A short stereoselective synthesis of (+)-(6R,2′S)-cryptocaryalactone via ring- closing metathesis

• Palakodety Radha Krishna,
• Krishnarao Lopinti and
• K. L. N. Reddy

Beilstein J. Org. Chem. 2009, 5, No. 14, doi:10.3762/bjoc.5.14

• the sub-classes of these 5,6-dihydro-2H-pyran-2-one compounds is the styryl lactones which possess a styryl moiety side chain. The styryl moiety of goniothalamin has been shown to be of importance for its cytotoxic effect on different cancer cells as well as its antimicrobial, larvicidal activity and

• ], (+)-obolactone (4) [29] and (+)-cryptofoline (5) [30] (Figure 1) are some of the naturally occurring styryl lactones. (+)-(6R,2′S)-Cryptocaryalactone (1) first featured in the phytochemical literature when its isolation from Cryptocarya bourdilloni GAMB (Lauraceae) was reported in 1972 by Govindachari [31][32

• 5,6-dihydropyrone ring of cryptocaryalactone. The advantage of this synthetic methodology is that one can in principle synthesize the other three diastereomers of cryptocaryalactone by altering the Sharpless epoxidation and Carreira’s conditions. Some natural products containing styryl lactones

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

• -THF, adjacent tetrahydrofuran-tetrahydropyran (THF-THP), nonadjacent THF-THP, mono-THP, and acetogenins containing only γ-lactones. These compounds are known to exhibit a broad range of biological activities, the precedent for which came from early South American populations, who used extracts of

• protocol for butenolide incorporation. Prepared from D-glutamic acid, lactone 102 was converted to the desired threo-trans-erythro THF isomer 103, which could be converted to the different two diolefins 104 and 105. The 14- (106) and 11-membered (107) ring lactones were obtained by an ester-tethered RCM

Phase- vanishing halolactonization of neat substrates

• Nicole Windmon and
• Veljko Dragojlovic

Beilstein J. Org. Chem. 2008, 4, No. 29, doi:10.3762/bjoc.4.29

• iodine failed, while iodolactonization of the corresponding disodium salt gave a mixture of γ- and δ-lactones [16]. However, no experimental details were given. Under phase-vanishing conditions, treatment of 14 with iodine gave the corresponding γ-lactone 16 in a moderate yield. The yield was inferior

Reactions of glycidyl derivatives with ambident nucleophiles; part 2: amino acid derivatives

• Gerald Dyker,
• Andreas Thöne and
• Gerald Henkel

Beilstein J. Org. Chem. 2007, 3, No. 28, doi:10.1186/1860-5397-3-28

• lactams 8 or 6-membered lactones 9 (Table 1). Most interestingly, the lactones 9 were always found as a single diastereoisomer, while for the lactams 8 various ratios of the diastereoisomers were detected (ratio ranging from 7:3 to 4:6, measured by 1H NMR). Under the strongly basic reaction conditions of

New modification of the Perkow reaction: halocarboxylate anions as leaving groups in 3-acyloxyquinoline- 2,4(1H,3H)-dione compounds

• Oldřich Paleta,
• Karel Pomeisl,
• Stanislav Kafka,
• Antonín Klásek and
• Vladislav Kubelka

Beilstein J. Org. Chem. 2005, 1, No. 17, doi:10.1186/1860-5397-1-17

• annulation of the fluorobutenolide cycle. An analogous Horner-Wadsworth-Emmons synthesis using ethyl (diethoxyphosphoryl)-fluoroacetate prepared from ethyl fluoroiodoacetate has been reported for the preparation of the α-fluoro-α,β-unsaturated acyclic esters and lactones. [14] However, when 1-benzyl-3-butyl

Stereoselective α-fluoroamide and α-fluoro- γ-lactone synthesis by an asymmetric zwitterionic aza-Claisen rearrangement

• Kenny Tenza,
• Julian S. Northen,
• David O'Hagan and
• Alexandra M. Z. Slawin

Beilstein J. Org. Chem. 2005, 1, No. 13, doi:10.1186/1860-5397-1-13

• conditions and resulted in N-(α-fluoro-γ-vinylamide)pyrrolidine products as homochiral materials in 99% de. These products were readily converted to their corresponding α-fluoro-γ-lactones by iodolactonisation and in good diastereoselectivity. Conclusion Molecules which have fluorine at a stereogeneic centre

• fluorinated substrates, to generate α-fluoro-γ-vinyl amides and then α-fluoro-γ-lactones as the end products after iodolactonisation. In 1998 Nubbemeyer[12][13] reported on such aza-Claisen rearrangements using the N-allylproline ester 1 and the N-allylpyrrolidine ether 2 with the acid fluoride of azidoacetic

• amines, to offer an alternative strategy to α-fluorocarbonyl compounds. Such products can be converted to γ-lactones by straightforward iodolactonisation.[14] γ-Lactones are a ubiquitious motif found in many natural product sand they are also useful templates for the synthesis of a wide range of bio

Towards practical biocatalytic Baeyer- Villiger reactions: applying a thermostable enzyme in the gram- scale synthesis of optically- active lactones in a two-liquid- phase system

• Frank Schulz,
• François Leca,
• Frank Hollmann and
• Manfred T. Reetz

Beilstein J. Org. Chem. 2005, 1, No. 10, doi:10.1186/1860-5397-1-10

• well versed in the use of enzymes. Keywords: Baeyer-Villiger oxidation; monooxygenases; two-liquid-phase system; stereoselective catalysis; biocatalysis; Introduction First reported in 1899, the Baeyer-Villiger (BV) reaction of ketones with formation of esters or lactones has become a fundamental and

• the practical biocatalytic preparation of enantiopure lactones based on BVMOs is proposed. Results and Discussion The commercially available rac-bicyclo [3.2.0]hept-2-en-6-one (1) is a common benchmark substrate for BVMOs. It is readily oxidized by CHMO in an enantioselective way and the products of

• after a reaction time of 24 h a conversion of 43% and moderate enantioselectivity for lactones (-)2 and (+)3 (Table 1). Conversion was drastically improved with mutants P1, P2, and P3 to more than 95% under the same whole-cell conditions, which clearly indicates enhanced enzyme activity. Additionally