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

Abstract

Treatment of 5-(tert-butyldimethylsilyl)-2,3-O-isopropylidene-D-ribose with lithium acetylides gave mixtures of syn-and antialkynols 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 web site for calculating the degree of chirality

“…Much of the richness of stereochemistry is lost with this black/white classification. Consider, for instance, the chiral substituted methylcyclohexanes (MC)13–16 (Scheme ): 1‐flouro‐3‐methylcyclohexane (1‐flouro‐3‐MC, say, axial ) is a representative chiral member of that family, but so is the 1‐deuterio derivative, which is only marginally different from the parent achiral MC. Chemical and physical intuition dictate that the “degree of chirality” of 1‐deuterio‐3‐MC is quite small with respect to the “degree of chirality” of 1‐fluoro‐3‐MC.…”