Stereoselective Synthesis of 2,4,6‐Trimethylcyclohex‐4‐ene‐1,3‐diol Derivatives and of polypropionate fragments with four contiguous stereogenic centers

Abstract

The Diels-Alder adduct (+)-3 of 2,4-dimethylfuran and 1-cyanovinyl acetate was converted stereoselectively into benzyl 6-(4-chlorophenylsulfonyl)-1,3-exo,5-trimethyl-7-oxabicyclo[2.2.l]hept-5-en-2-exo-yl (26) and -2-endo-yl ether (36). Addition of LiAIH, to the latter led to the 3-0-benzyl derivatives 28 and 37 of (IRS,2SR,3SR, Introduction. -In the preceding paper [2], we demonstrated that the optically pure Diels-Alder adducts (+)-1 and (-)-2 (naked sugars of the second generation) [3] of 2,4-dimethylfuran [4] to 1 -cyanovinyl (1 R)-camphanate and (1 S)-camphanate, respectively, can be converted with high stereoselectivity into polypropionate fragments with four or five contiguous stereogenic centers. Cross-aldolisations with 7-oxabicyclo-[2.2.l]heptan-2-ones allowed one to generate long-chain polypropionate fragments containing up to eleven contiguous stereogenic centers and tertiary-alcohol moieties. The method relies on the high exo-face selectivity of the reactions of endocyclic n functions of the 7-oxabicyclo[2.2. llheptene systems [5] and on the high regioselectivity of the Bueyer-

Highly-functionalised difluorinated cyclohexane polyols via the Diels–Alder reaction: regiochemical control via the phenylsulfonyl group

“…Episulfonium ion ring opening with proton loss was observed before by Bialecki and Vogel. 24 We observed none of the allylic sulfide from the endo-cycloadduct indicating that formation of the 5-membered lactone is fast on the timescale of episulfonium ion ring opening, but that formation of the six-membered cyclic carbonate cannot compete with proton loss. Though the carbamoyloxy group is Lewis basic, the extra degree of rotational freedom appears to be enough to lower the rate below that of the eliminative ring opening (there are additional issues with restricted rotation in the carbamoyloxy group which may impede access to conformations from which cyclisation can occur).…”

“…Purification by column chromatography (20% ethyl acetate in hexane) afforded an inseparable mixture of cycloadducts 7e and 8e (1.9 : 1) as a colourless oil (0.66 g, 96%); R f (20% ethyl acetate in hexane) 0.35; d H (300 MHz, CDCl 3 ) 6.33 (1H, d, J 5.4, HC=CH (major cycloadduct)), 6.25-6.19 (3H, m, HC=CH), 4.21 (2H, q, J 7.2, OCH 2 CH 3 (minor stereoisomer)), 4.10 (2H, q, J 7.2, OCH 2 CH 3 (major stereoisomer)), 3.34-3.12 (4H, m, N(CH 2 CH 3 ) 2 ), 1.50 (3H, s, CH 3 ), 1.46 (3H, s, CH 3 ), 1. 24…”

Au(I)-Catalyzed Ring Expanding Cycloisomerizations: Total Synthesis of Ventricosene

“…The reduction of 19 was accomplished using K-selectride in a mixture of ethanol and THF at −78 °C,18 providing alcohol 20 as a single diastereomer. With the hydrocarbon skeleton of ventricosene fully assembled, we turned our attention to the deoxygenation of 20 .…”

Citric acid mediated catalytic osmylation/oxidative cleavage of electron deficient olefins: a vinyl sulfone study

“…These features are clearly apparent in the regio-and enantiospecific Jacobsen epoxidation of the terminal olefin of 6-and 7-membered 1,3-dienyl phenyl sulfones (>99% de and ee), leading to the genesis of our polypropionate method. [16][17][18] Earlier strategies for dealing with the oxidative inertness of vinyl sulfones originally involved reductive cleavage of the sulfone moiety via treatment with BuMgCl/Pd(II)OTf, 19 or Na amalgam. 20 The resulting electron-neutral olefin can then be readily cleaved, but the transformation sacrifices the inherent olefin dissymmetry.…”