TRIFLATE MESYLATE RATIOS AND COMPETING C-O AND S-O BOND CLEAVAGES IN NUCLEOPHILIC VINYLIC SUBSTITUTION/

In an attempt to develop the k(OTf)/K-OMs ratio as a mechanistic tool for the ''addition-elimination'' route in nucleophilic vinylic substit ution, several pairs of vinyl mesylates and triflates were prepared. W hereas reactions of ArC(LG)=C(CO(2)Et)(2) (LG = OTf, OMs) with piperid ine and morpholine in MeCN or THF gave the normal substitution product with k(OTf)/k(OMs) ratios of 4.3-10.6, the reaction of the mesylates, Ar = p-O2NC6H4, and of PhC(OMs)=C(Me)CN with MeS(-) gave a ketone via an S-O bond cleavage. A related mesityl-substituted tosylate also rea cted with p-MeC(6)H(4)X(-) (X = O, S) via an S-O bond cleavage. Hence, k(OTf)/k(OMs) ratios cannot be used as a general mechanistic tool. Se veral reactivity ratios in vinylic substitution are briefly discussed.