Cyclization of terpenoid polyalkenes via photo-induced electron transfer - Versatile single-step syntheses of mono- and polycycles

Light-induced radical cationic cyclizations of suitably functionalized polyalkenes, readily available from geraniol, all-trans-farnesol and all-trans-geranylgeraniol, establish a powerful access to mono- and polycyclic compounds. Within these highly stereo- and chemoselective transformations, the cyclization mode, optionally yielding five- and six-membered rings, is efficiently controlled by the substitution pattern of the polyalkenes (acetate vs. alpha,beta-unsaturated ester and dicyano groups). In all examples, protic solvents add highly stereoselectively to the omega-alkene site of the isoprenoid starting materials in anti-Markovnikov sense suggesting that radical cation intermediates are intercepted. Notably, these transformations achieved upon light-induced electron transfer mimic tn vivo processes of non-oxidative cationic terpene cyclizations.