Selective chlorination with methanesulfonyl

Synthesis of dienyl chloride 2.349, the dithiane coupling partner for dithiane aldehyde 2.338, was accomplished in five steps from commercially available cis-2-butene-l,4-diol (Scheme 2.72). To this end, monosilylation of 2.344 as the TBS ether and this allyl alcohol was then oxidized with accompanying Zto E isomerization by PCC [122] to afford the enal 2.346 in 73 % yield. a,]S-unsaturated ester 2.347 was accessed by the Still—Gennari modification [219] of the Homer-Wads worth-Emmons olefination in good yield and selectivity (92 %, Z/E — 16 1). Reduction of the resulting ester 2.347 to produce allyl alcohol 2.348, in turn was chlorinated by treatment with LiCl and methanesulfonyl chloride to furnish the requisite dienyl chloride 2.349. 

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