Catalyst and ring size effects on periselectivity of oxonium ylide rearrangements.
Diazoketones were subjected to carbene-transfer with Rh(II) or Cu(II) catalysts to probe the selectivity for rearrangement via five- or six-membered oxonium ylides. 4,5-Bis(benzyloxy) and 4-allyloxy-5-benzyloxy substrates 3a,b showed a large preference for rearrangement via the five-membered ylide under all conditions. However, a sharp divergence was seen with 5-allyloxy-4-benzyloxy substrate 3c, which underwent predominantly a [2,3]-shift to pyran 5c via the six-membered ylide with Cu(II) catalysis and a [1,2]-shift to furan 4c via the five-membered ylide with Rh(II) catalysis.
Marmsäter
Fredrik P
FP
Department of Chemistry, University of Alberta, W5-67 Gunning-Lemieux Chemistry Centre, Edmonton, AB T6G 2G2, Canada. fredrik.west@ualberta.ca
Vanecko
John A
JA
West
F G
FG