carbonium character. However, conjagation of the carbonyl group with the developing double bond should, in terms of the E 2 mechanism, provide a strong driving force. This should be especially powerful in elimination from XX because conjugation of -zwith -CO-would be established in the transition state. Moreover, these reactions conform to the trans-stereoelectronic pattern characteristic of E 2 reactions [60,61]. [60] H. B. ilther and T. Reichstein, Helv. Chim. Acta 26, 492 (1943); E. Seebeck and T . Reichstein, ibid. 26, 536 (1943). [61] N.