Stereoselective preparation of chiral building blocks having 1,3-syn-dimethyl group from D-glucose

Reaction of (2S,3R,5S,6S)-2-methoxy-3,5-dimethyl-tetrahydro-2H-pyran-6-carbaldehyde (a-8) with MeMgCl gave (6'S)-α-9 as a single isomer which was converted into (5S,6R)-epoxide (cis-12) by a sequence of reactions involving tosylation, ring-opening by the reaction with HS(CH 2 ) 3 SH, and treatment with NaOMe. When α-8 and its β-anomer (β-8) respectively reacted with MeTi(Oi-Pr) 3 and the resulting alcohols were subjected to similar transformation as above, (55,65)-epoxide (trans-12) was obtained irrespective of the anomeric configuration. The reaction of trans-12 with lithium alkynylaluminates 13a and 13b took place at the position 6 to afford the corresponding alkynes 14a and 14b.