Optically pure (S)-cyclopent-2-en-1-ol and (S)-3-methoxycyclopentene

Abstract

Optically pure (S)-cyclopent-2-en-1-ol, [Formula: see text] (c 1.1, CHCl3), and (S)-3-methoxycyclopentene, [Formula: see text] (c 3.86, n-hexane), were prepared from ethyl (1R,2S)-2-hydroxycyclopentanecarboxylate, which is readily available by yeast reduction of ethyl 2-oxocyclopentanecarboxylate. The optical purity of the alcohol was determined from its Mosher ester, and that of the ether by gas chromatography using a Ni-4-Pin column. Keywords: (S)-cyclopent-2-en-1-ol, (S)-3-methoxycyclopentene.

Highly Enantioselective Copper−Bisoxazoline-Catalyzed Allylic Oxidation of Cyclic Olefins with tert-Butyl p-nitroperbenzoate

“…Yields were moderate for the purified ester products; however, the ligands could be recovered in 85% yield based on the amount used and recycled. In all cases the S,S ligands generated ( S )-ester product . The cyclohexenyl ester was obtained with very high 96% ee selectivity using the diphenyl gem-dimethyl bisoxazoline (entry 3).…”

Palladium-Catalyzed Enantioselective Allylic Alkylation of Thiocarboxylate Ions: Asymmetric Synthesis of Allylic Thioesters and Memory Effect/Dynamic Kinetic Resolution of Allylic Esters

“…We had previously noted a similar change of the sign of optical rotation in the case of the corresponding seven- and eight-membered cyclic tert -butyl sulfones, which both had the same absolute configuration 1e. The absolute configurations of acetates ( S )- 2-OMoc ,1e ( S )- 1-OAc ,26a ( R )- 6-OAc ,26c and ( R )- 7-OAc ,26d carbonate ( R )- 8-OMoc ,1e and alcohols ( S )- 5-OH 26e and ( S )- 6-OH 26b were assigned on the basis of their chiroptical data.…”

“…This problem could be overcome, however, by the use of the more reactive KSBz instead of KSAc. Here, at 56% conversion of rac - 1-OAc the thiobenzoate ( R )- 1-SBz of 83% ee was isolated in 53% yield (entry 5) and the acetate ( S )- 1-OAc 26a of 99% ee was recovered in 22% yield. The low yield of ( S )- 1-OAc was due to considerable losses encountered during isolation of the acetate because of its volatility.…”

Synthesis of Isopeptide Epoxide Peptidomimetics

“…In developing a strategy for the synthesis of target olefin isosteres of the γ-glutamyl dipeptide (e.g., 6 ), and the corresponding internal epoxide derivatives (e.g., 4) , the two important synthetic challenges in the molecules that need to be addressed are, (i) stereospecific generation of the chiral center which serves as a pseudo α -carbon in the C -terminal glutamic acid replacement, analogous to the 2 S or 2 R stereochemistry in the parent isopeptide, and (ii) selective formation of the E -olefin during synthesis of the olefinic dipeptide isostere. Stereospecific generation of either stereoisomer at C-1 of the cyclopent-2-ene derivative, 8 or ent - 8 , from ethyl 2-oxocyclopenane carboxylate, 9 , has been achieved via lipase-mediated ester hydrolysis13,19-21, or a dynamic kinetic resolution,22 respectively, (Scheme 1) leading ultimately to the “ l -Glu-γ- l -Glu” mimetic, 4 , and the “ l -Glu-γ- d -Glu” mimetic, 5 . The desired E -olefin is most consistently achieved by the Julia-Kocienski reaction through the olefination of an aldehyde (e.g., 7 ) 23,24.…”

“…In developing a strategy for the synthesis of target olefin isosteres of the γ-glutamyl dipeptide (e.g., 6 ), and the corresponding internal epoxide derivatives (e.g., 4) , the two important synthetic challenges that need to be addressed are (i) stereospecific generation of the chiral center which serves as a pseudo-α-carbon in the C -terminal glutamic acid replacement, analogous to the 2 S or 2 R stereochemistry in the parent isopeptide, and (ii) selective formation of the E -olefin during synthesis of the olefinic dipeptide isostere. Stereospecific generation of either stereoisomer at C-1 of the cyclopent-2-ene derivative, 8 or ent - 8 (10) , from ethyl 2-oxocyclopenane carboxylate, 9 , has been achieved via lipase-mediated ester hydrolysis, ,− or a dynamic kinetic resolution, respectively (Scheme ). The desired E -olefin is most consistently achieved by the Julia−Kocienski reaction through the olefination of an aldehyde (e.g., 7 ). , As outlined in Scheme , the critical stereoselective synthesis of 10 , via sequential dynamic kinetic resolution, xanthate formation, and pyrolysis to form the desired cyclopentene derivative proceeded in higher yield (65%, 5 steps) than the synthesis of 8 via acetylation, hydrogenation of the enol acetate, lipase-catalyzed resolution, and pyrolysis of the enantiomeric xanthate (21%, 7 steps) .…”