FACE SELECTION IN CLAISEN REARRANGEMENTS

An investigation is reported of the stereochemistry of the Claisen rea rrangement of 2-(5-phenyl-2-adamantylidene) ethyl vinyl ether (1-Ph) a nd of allyl (5-fluoro-2-adamantylidene) methyl ether (2-F). Both ether s undergo the rearrangement principally with the newly forming bond at the zu face (i.e., syn to the 5-substituent), showing that this bond in the transition state is electron deficient from the standpoint of b oth termini. The two derivatives of the latter ether in which the one remaining hydrogen has been replaced by a phenyl group or an oxide ani on function (3-F and 4-F) were also examined. In these two instances a s well, the zu face of the vinyl terminus is favored; in all four case s, the ratio of stereoisomers is in the range of 1.33 to 1.56. The int roduction of a negative charge at this terminus evidently fails to bri ng about the onset of the type of delocalization envisioned in the Anh model. Taken together with the oxy-Cope and allyl vinyl sulfoxide rea rrangements studied earlier, these [3,3] sigmatropic shifts all exhibi t a remarkably uniform face selectivity.