Stereodivergent synthesis of 5a-carba-hexopyranoses from carbohydrates via 6-exo-dig radical cyclization: preparation of 5a-carba-β-d-manno-, α-d-allo-, β-l-talo- and α-l-gulopyranose pentaacetates from d-mannose

Synthesis of chiral cyclohexanes and carbasugars by 6-exo-dig radical cyclisation reactions

Treatment of 5-(tert-butyldimethylsilyl)-2,3-O-isopropylidene-D-ribose with lithium acetylides gave mixtures of syn- and anti-alkynols 2a–2c which were separated following protection as methoxymethyl ethers. These were converted to the corresponding iodides which underwent 6-exo-dig radical cyclisation to afford chiral cyclohexanes and carbasugars. Oxidation of the primary alcohols 6a–b gave the corresponding aldehydes which on treatment with Grignard reagents afforded a mixture of alcohols. The corresponding iodides underwent similar 6-exo-dig cyclisation to give fully functionalised cyclohexanes.

A de novo approach to C-branched inositols: synthesis of a myo-inositol precursor for C-linked glycosyl phosphatidylinositols

C-Linked glycosyl inositols are valuable structure-activity probes because of their greater hydrolytic stability and different conformational behavior compared with their parent O-glycosides. Simple C-branched inositols are synthetic precursors to these and other groups of inositol mimetics. Herein is described a de novo synthesis of C-branched inositols that contain a versatile ethenyl side chain for elaboration into more complex appendages. The approach centers on a stereoselective oxocarbenium ion-allylsilane cyclization and provides C-branched inositols with different stereochemical motifs. The synthesis of C-ethenyl-di-O-isopropylidene-myo-, neo-, epi-, and allo-inositols is discussed.

Synthesis of 2,3:4,6-di-O-isopropylidene-d-allopyranose from d-glucose

2,3:4,6-Di-O-isopropylidene-d-allopyranose can be conveniently prepared from d-glucose via a synthetic sequence, which includes Mitsunobu inversion at O-3, di-O-isopropylidenation of phenyl-1-thio-d-alloside and anomeric deprotection on treatment with NBS/CaCO3.