The First Ring-Enlargement of a l-Azabicyclo[1.1.0]butane to a l-Azabicyclo[2.1.1]hexane

摘要

The reactions of 3-phenyl-l-azabicyclo[1.1.0]butane (4) with dimethyl dicyanofumarate ((E)-8) and dimethyl dicyanomaleate ((Z)-8) lead to the same mixture of cis- and trans-4-phenyl-l-azabicyclo[2.1.1]-hexane 2,3-dicarboxylates (cis-11 and trans-11,resp.;Scheme 3).This result of a formal cycloaddition to the central C-N bond of 4 is interpreted by a stepwise reaction mechanism via a relatively stable zwit-terionic intermediate 10,which could be intercepted by morpholine to give a 1:1:1 adduct 12,which undergoes a spontaneous elimination of HCN to yield the fumarate 13 (Scheme 4).