Ta. Engler et al., CONTRASTING REACTIVITY IN LEWIS ACID-PROMOTED REACTIONS OF THIO-ALLENES AND SILYL-ALLENES WITH 1,4-BENZOQUINONES, Tetrahedron letters, 37(3), 1996, pp. 327-330
In Ti(IV)-promoted reactions with 2-methoxy-1,4-benzoquinones 3, thioa
llenes I give 2+2 and/or 3+2 products via attack on a C=C moiety of th
e quinone, whereas silylallene 2 gives products derived from attack on
a carbonyl group of the quinone.