The rates of cyclizations of the aminyl radicals were measured (2a : k(1) = 5.1 x 10(5) s(-1) 2b : k(1) = 3.1 x 10(4) S-1). The angle strains slow down the ring closures. The cyclizcd oxy radicals 3a and 3b then undergo beta-scission to give 4a and 4b with the rates (3a : k(2) = 6.5 x 10(8) s(-1), 3b : k(2) = 1.0 x 10(7) s(-1)).