Oxazaborolidine-Catalyzed Enantioselective Reduction of α-Methylene Ketones to Allylic Alcohols

Investigation on the synthesis of 24-(R)-hydroxycholesterol

A facile and novel strategy has been developed for synthesis of 24-(R)-hydroxycholesterol, a key intermediate of tacalcitol, starting from 24-dehydrocholesterol in seven steps with 48.2% overall yield and high diastereomer ratio. Photocatalytic oxidation of olefins by employing inexpensive Rose Bengal as photosensitizer and air as the sole oxidant for the preparation of Δ^5,25-3β-Hydroxycholestadiene-24-one-3-acetate is the key step in this synthetic route. This developed strategy features mild conditions, satisfied total yield and excellent stereoselectivity (24-R/S = 97.7:2.3), providing a novel access to the 24-(R)-hydroxycholesterol.

Formal enantioselective total synthesis of bisdehydroneostemoninine

A formal enantioselective total synthesis of bisdehydroneostemoninine employing L-glutamic acid as the chiral pool is described. The key features of the synthesis include regioselective and enantioselective opening the chiral epoxide with dimethylsulfonium methylide and tandem Friedel-Crafts cyclization followed by lactonization to form the 5-7-5 tricyclic core of the target stemona alkaloids. The synthetic route provides opportunities to explore the biological behavior of enantiopure bisdehydroneostemoninine. [Formula: see text].

Synthetic strategies towards mycolactone A/B, an exotoxin secreted by Mycobacterium ulcerans

Pitfalls and dead-ends pave the way to mycolactone A/B. This full account reports synthetic efforts towards this natural product that eventually culminated in a de novo total synthesis.

A highly stereoselective synthesis of C-24 and C-25 oxysterols from desmosterol

A new highly stereoselective construction of the side chain of the C-24 and C-25 oxysterols has been achieved by using desmosterol acetate as the starting material and an improved Sharpless catalytic asymmetric dihydroxylation with 100% d.e. (diastereomeric excess) as the key step. The result is much better than the usual asymmetric dihydroxylation procedure. t-Butyl nitrite/2,2,6,6-tetramethylpiperidine N-oxyl radical/FeCl3 catalyst system was developed to activate molecular oxygen for the aerobic oxidation of 24-hydroxycholesterol and the 24-ketocholesterol was obtained in 86.2% yield. The oxidation system has never been reported before. The mechanism for the catalytic aerobic oxidation was also proposed.

Stereoconvergent route to chiral cyclohexenone building blocks: formal synthesis of (-)-dysidiolide

A stereoconvergent access to chiral carbocyclic building blocks is reported. 6-(3'-Hydroxy-4'-methylpent-4'-enyl)-3-methoxy cyclohex-2-enone () that consists of four stereoisomers, i.e., racemic ca. 1 : 1 diastereomers, is converted to enantiomerically pure carbocycles through a combination of regioselective catalytic asymmetric reduction and alkylative remote stereoinduction. The present stereoconvergent strategy has allowed the formal synthesis of bioactive (-)-dysidiolide.