Interaction of Trimethylsilyl and Trimethylstannyl Substituents with C−O Bonds at the γ Position. Results from X-ray Structural Studies and Solvolysis Studies
作者:Alison J. Green、Tracey Pigdon、Jonathan M. White、Joseph Yamen
DOI:10.1021/jo9723265
日期:1998.6.1
Accurate X-ray structural studies have been carried on the gamma-Me3M (M = Si, Sn)-substituted cyclohexyl esters 21-Ns, 22-Ns, 23-Ns, 24-PNB, and 24-PNB. Analysis of the structural parameters reveals that the C(alkyl)-O(ester) bond distance is lengthened slightly compared to nonmetal-substituted analogues provided that the C-M, C-O, and intervening C-C bonds are in the W arrangement as is the case for 22-Ns, 23-Ns, and 24-Ns. However, the C-O bond distances for 22-PNB and 22-Ns, which do not have the W geometry, are not significantly lengthened. These structural effects are consistent with the presence of a percaudel interaction between the back lobe of the C-M sigma bond and the C-O sigma* orbital. The gamma-Me3Sn cyclohexyl nosylates 21-Ns and 23-Ns undergo unimolecular solvolysis in 97% TFE/H2O with relative rates ca. 1:>10 000.