Allyl Tebbe methylenation

Tebbe methylenation < 1978JA3611 > of a-bromoacetophenone resulted in the formation of allylic bromide 165, which upon reaction with benzenesulfonamide gave the 1,6-diene 166 (Scheme 35). The acyclic diene 166 underwent photooxidative cyclization to form 1,2,5-dioxazepine 167 <1996TL815>. 

The asymmetric total synthesis of the putative structure of the cytotoxic diterpenoid (-)-sclerophytin A was realized via a Tebbe-Claisen rearrangement of a tricyclic lactone precursor in the laboratory of L.A. Paquette/ The tricyclic lactone was subjected to the Tebbe methylenation protocol to provide the allyl vinyl ether that was then heated to 130-140 °C in p-cymene to undergo the Claisen rearrangement in good yield. 

Before tethering can be attempted, the 2-0-allyl group must first be iso-merised to a vinyl ether. Isomerisation was accomplished by treating glycosyl fluoride 74 with Wilkinson s catalyst and n-butyl lithium, which afforded vinyl ether 75 in an excellent yield of 96%. It is important to note that the Wilkinson s catalyst mediated isomersiation is very efiicient when compared to the previously used and capricious Tebbe methylenation methodology. Subsequent NIS-mediated tethering of secondary acceptor 76 to vinyl ether 75... 

Oxidative cleavage of C-allyl mannose 419 [157] following Wong s procedure [158] leads to acid 420 which is esterifled with 418 prior to methylenation with Tebbe s reagent (O Scheme 83). 

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