Two new methods for the ring expansion of cyclic ketones via an alkylidenesulfonium and an episulfonium ion intermediate have been developed. The α,β-doubly deprotonated dianion of phenylthionitromethane is readily added to cyclic ketones and subsequent rearrangement of the resulting adducts proceeds well in the presence of aluminum chloride to afford the ring expanded α-phenylthio ketones via aluminum chloride mediated denitration.
Tert-Butyldimethylsilyl ethers of 1-vinyl-1-cyclo-alkanols have been also found to be rearranged, upon successive treatment with benzenesulfenyl chloride and silver tetrafluoroborate, to produce the ring expanded α-(1-phenylthioalkyl) ketones via an episulfonium ion intermediate.
The synthetic utilities of magnesium bromide and boron tribromide have been investigated. Magnesium bromide can be utilized as a mild and efficient reagent for the selective cleavage of tetrahydropyranyl ethers in the presence of tertbutyldimethylsilyl ethers. Selective conversion of acetals into thioacetals, monothioacetals, α-alkoxyazides, and α-alkoxyalkyl thioacetates have been performed successfully with magnesium bromide in the presence of appropriate nucleophiles such as thiols, hydrozoic acid, and thiolacetic acid.
Boron tribromide has been found to be effective for the direct conversion of tert-butyldimethylsilyl and tert-butyldiphenylsilyl ethers into alkyl bromides. This reaction is believed to proceed via a dual mechanism involving complex formation from TBDMS ethers and boron tribromide followed by internal nucleophilic displacement ($S_Ni$) along with $S_N1$.
환상케톤의 새로운 고리확대 방법으로 알킬리텐술포니움 이온과 에피술포니움 이온을 중간체로 하는 두 가지 방법에 대해 연구하였다. 페닐티오니트로메탄의 α, α-이중 음이온은 환상케톤에 용이하게 첨가 되며, 생성된 첨가물은 염화 알루미늄 존재하에서 쉽게 자리옮김 반응을 하여 α-페닐티오 케톤을 생성하였다. 1-비닐-1-시클로알칸올의 tert-부틸디메틸실릴 에테르에 염화벤젠술페닐과 사플루오로 붕산 은을 연속적으로 가해주면, 에피술포니움 이온 중간체를 거쳐 쉽게 자리옮김 반응이 일어나 α-(1-페닐티오알킬) 케톤이 생성되었다. 위의 두 방법 모두 비대칭 케톤의 경우, 전이상태의 전자결핍을 가장 효과적으로 안정화시켜 주는 탄소가 선택적으로 이동하 였다.
