Mesy lation

The AT-Boc-lactam 107 was submitted to a three-step sequence (Scheme 31). First, a Grignard addition allowed the installation of the vinyl moiety, then the unsaturated ketone intermediate was reduced and after mesy-lation, the alcohol underwent a diastereoselective cyclization to provide the five-membered ring 108. The latter was then converted into the A -Cbz pyrrolidine 109 which was transformed into aldehyde 110 via a 1,2-diol oxidative cleavage. The aUylation of 110, under Reformatsky type conditions, then gave a mixture of separable diastereoisomers 111a and 111b (d.r. 79 21). 

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