An investigation is reported of the stereochemistry of the Claisen rearrangement of 2-(5-phenyl-2-adamantylidene) ethyl vinyl ether (1-Ph) and of allyl (5-fluoro-2-adamantylidene) methyl ether (2-F). Both ethers 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 both termini. The two derivatives of the latter ether in which the one remaining hydrogen has been replaced by a phenyl group or an oxide anion function (3-F and 4-F) were also examined. In these two instances as well, the zu face of the vinyl terminus is favored; in all four cases, the ratio of stereoisomers is in the range of 1.33 to 1.56. The introduction of a negative charge at this terminus evidently fails to bring about the onset of the type of delocalization envisioned in the Anh model. Taken together with the oxy-Cope and allyl vinyl sulfoxide rearrangements studied earlier, these [3,3] sigmatropic shifts all exhibit a remarkably uniform face selectivity.
of the 19F substituent chemical shifts (SCS) against polar field parameters (σF) together with comparisons against the 19F SCS of 4‐substituted(X)bicyclo[2.2.2]oct‐1‐yl fluorides (1) provide unequivocal evidence for the importance of electrostatic field and ‘through‐three‐bond’ electron delocalization (double hyperconjugation) effects as long‐range modes of transmission of polar effects in these saturated
作者:Ashis Mukherjee、Qianhong Wu、William J. le Noble
DOI:10.1021/jo00091a010
日期:1994.6
An investigation is reported of the stereochemistry of the Claisen rearrangement of 2-(5-phenyl-2-adamantylidene) ethyl vinyl ether (1-Ph) and of allyl (5-fluoro-2-adamantylidene) methyl ether (2-F). Both ethers 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 both termini. The two derivatives of the latter ether in which the one remaining hydrogen has been replaced by a phenyl group or an oxide anion function (3-F and 4-F) were also examined. In these two instances as well, the zu face of the vinyl terminus is favored; in all four cases, the ratio of stereoisomers is in the range of 1.33 to 1.56. The introduction of a negative charge at this terminus evidently fails to bring about the onset of the type of delocalization envisioned in the Anh model. Taken together with the oxy-Cope and allyl vinyl sulfoxide rearrangements studied earlier, these [3,3] sigmatropic shifts all exhibit a remarkably uniform face selectivity.