Septanose glycals

SCHEME 13.10 Photo-cycloisomeiizations to prepare (a) septanose glycal 37 [23] and (b) oxepinone 39 [24]. 

M. W. Peczuh and N. L. Snyder, Carbohydrate-based oxepines Ring expanded glycals for the synthesis of septanose saccharides, Tetrahedron Lett., 44 (2003) 4057—4061. 

Only a few attempts at nucleophiHc substitution reactions with educts derived from (conformationally flexible) septanoses are known [76]. As can be seen from Table 10, besides straight Sn2, only elimination reactions have been reported [77]. Of interest is that in attempted substitutions of the epimeric 5-tosylates 103 and 105 (entries 1-3), the E[5,H-4] reaction (to give 104 containing a bridge head double bond) is preferred over the E[5,H-6] mode (which produces the glycal type 106) however, the latter product predominates when bulky bases (f-BuOK in f-BuOH, entry 4) are applied. 

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