Competing [3+4]‐ and [2+4]‐Cycloadditions of Allenyl Cations

Abstract

A facile synthesis of bicyclo[3.2.1]octa-2,6-dienes (3), R1 = alkyl, and 5-(aryl-methylene)norbornenes (4), R1 = aryl, is possible by cycloaddition of allenyl cations (2) to cyclopentadiene. (2) was generated from propargyl halides (1) with catalytic amounts of ZnCl2 in ether/CH2Cl2.