2,3-Unsaturated allyl glycoside preparation

The addition of thiols and sulfonyl derivatives to unsaturated compounds under radical conditions represents a mild method to prepare sulfides and sulfones in high yield and with antr-Markovnikov orientation [8-9]. Recent examples have been reported in carbohydrate chemistry. Thioacetic acid and thiols react with exocyclic glycals 2 [22a] and with allyl a- and /i-glycosides 3 [22b] to give sulfur functionalized derivatives to be used as intermediates for the synthesis of biologically active compounds. 

Claisen rearrangement of 3,4-unsaturated glycosides to C4-branched derivatives provided useful intermediates for the total synthesis of thromboxanes (Scheme 20). First reported independently by Corey et al. [41] and Hernandez [42],both the Eschenmoser amide acetal and the Johnson orthoester procedure afforded good results for the conversion of allylic alcohol 99 (R = Me, R = H) to the respective amide or ester 100. Corey et al. further transformed the former compound to lactone 101, previously described as a precursor for the total synthesis of thromboxane B2 (102). A number of further derivatives 100 (R = allyl, R = H or TBDMS, R = NMe2 or OEt) and its C2-epimer were prepared in a similar manner during later thromboxane synthetic studies [43,44]. 

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