Highly Strained Bicyclic Systems. VI.1Reactions of 1,5,5-Trimethylbicyclo[2.1.1]-hexane-6-carboxylic Acid and the Synthesis of Bicyclo[2.1.1]hexyl Analogs of Borneol and Isoborneol2
Citral (I) is cyclized by UV irradiation1 to 2-isopropenyl-5-methylcyclopentane-carboxaldehyde (II), containing the carbon skeleton of the monoterpenes of ants and catmint. 1,6,6-Trimethylbicyclo[2,1,1]hexane-2α-carboxaldehyde (XII, R = H), produced in lesser amount at the same time, was synthesized from camphor. The two photocitrals may, perhaps, come from a common intermediate containing the cyclopentane