Neighbouring-group Influence on the Ring Opening of 2-Aryloxymethyl-1,1,2-tribromocyclopropanes under Phase-transfer Conditions.
摘要:
When a number of 2-aryloxymethyl-1,1,2-tribromocyclopropa were treated with sodium hydroxide and ethanol under phase-transfer conditions, ring opening occurred to give mixtures of acetylenic diethyl acetals and ketals in better than 80% total isolated yield. The acetylenic diethyl ketals predominated significantly and were, in some cases, almost the exclusive product. It is argued that this ketal selectivity is in part caused by hydrogen bonding between ethanol and the aryloxy group.
The reaction of 2-chloro-allyl acetate with sodium ethyl acetoacetate in the presence of a platinum(O) complex gave furan derivatives. The key feature of this-new platinum-catalyzed reaction is the nucleophilic substitution at the central carbon atom of pi-allyl complexes. The regioselectivity of the nucleophilic attacks (central or terminal) is dependent on the pK(a) of the nucleophile. In addition, a labeling experiment revealed that a rapid syn-anti isomerization of the (pi-allyl) platinum complexes occurs.