Allylic diethylboranes are obtained from 1-methylcycloalkenes and 2-alkenes, respectively, via metalation with trimethylsilylmethylpotassium (generated in situ from bis(trimethylsilylmethyl)mercury and potassium sand) and subsequent reaction with chlorodiethylborane. The allylic boranes react diastereoselectively with aldehydes to give homoallylic alcohols. The alcohols are oxidized with pyridinium dichromate to β,γ-unsaturated ketones, which in turn are isomerized with aluminum oxide to conjugated ketones. The transformation provides access to 2-methylene-1-acylcycloalkanes, 3-acyl-1-alkenes and 3-acyl-2-alkenes not readily available by Friedel-Crafts acylation of olefins.
烯丙基
二乙基硼烷分别由1-甲基环
烷烃和2-烯烃通过三甲基
硅甲基
钾(由双(三甲基
硅甲基)
汞和
钾砂原位生成)
金属化,然后与
二乙基硼烷反应而制得。烯丙基
硼烷与醛发生非对映选择性反应,生成同
烯丙醇。这些醇与
重铬酸吡啶氧化为2,3-不饱和酮,后者与氧化铝发生异构化反应,生成共轭酮。通过这种转化,可以得到2-亚甲基-1-酰基环
烷烃、3-酰基-1-烯烃和3-酰基-2-烯烃,这些物质无法通过烯烃的傅克酰化反应获得。