Studies on Intramolecular Alkylation, XI. An Adventitious Synthesis of a 1,4-Ethanopentalene Derivative from a Norbornenone-Derived Diazomethyl Ketone

The C2-epimeric mixture of 2-chloro-7-formylbicyclo[2,2,1]hept-5-ene-2-carbonitriles (5) was homologated by simple synthetic steps to the norbornenone-derived acids (12) and (13). The diazomethyl ketone derived from (12), on treatment with BF3,Et2O in nitromethane, gave (lα(,3aβ,4α(,6aβ)-3,3a,4,6a-tetrahydro-1,4-ethanopentalene-2(1H),8-dione (20). Structure (20) was deduced from cleavage by sodium methoxide to a symmetrical methyl ester derived from bicyclo-[3,2,1]oct-6-en-3-one. The structure of the reported product dione (8) from the acetic acid treatment of diazoketone (7) has been revised to (21).