ring junction. Four-carbon ring expansion shows stereoselectivity favoring the trans-fused product 6-trans. The radical precursor cyclobutanones are readily prepared by intramolecular [2 + 2] cycloaddition of ketenes or keteniminium salts to olefins.
稠合
环丁酮的自由基环扩环得到双环酮,该环扩环了三个和四个碳原子,且羰基β连接至环结。四碳环膨胀显示出有利于反式稠合产物6-trans的立体选择性。自由基前体
环丁酮易于通过烯酮或烯酮
铵盐的分子内[2 + 2]环加成反应而制得。