Orthopropionic acid, methyl-3-phenylsulfonyl

The a,j5-unsaturated -lactone 1107 is constructed by Ghosez s methodology, which involves treating the epoxide with the lithio anion of methyl-3-phenylsulfonyl orthopropionate followed by acid hydrolysis and DBU-induced elimination. Reduction of the lactone to a lactol with diisobutylaluminum hydride and subsequent C-glycosidation furnishes aldehyde 1108 with a 4 1 epimeric ratio. This is then carried on to the desired fragment 1109. 

This reaction was first reported by Ghosez and co-workers in 1988. It is the synthesis of a./S-unsaturated 5-lactone and the corresponding dihydropyran reduced fi om such lactone derivative, involving the reaction of epoxide with the lithio derivative of methyl 3-(phenylsulfonyl)orthopropionate and subsequent acid hydrolysis and base-induced elimination of phenylsulflnic acid. This reaction is thus known as the Ghosez cycUzation or the Ghosez lactonization. ... 

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