A new synthetic method has been developed for preparing azoalkanes bearing geminal α-cyano and α-trimethylsiloxy groups. While the symmetrical compound 5 decomposes near room temperature to afford, almost entirely, the C−C dimers, the unsymmetrical azoalkane 3 requires heating to 75 °C. The thermolysis activation parameters of 3 and 5 can be rationalized on steric grounds without invoking captodative radical stabilization. A 13C NMR product study of photolyzed 3 in the presence of TEMPO at 21 °C shows that the fate of caged [tert-butyl, 1-trimethylsiloxy-1-cyanoethyl (14)] radical pairs is disproportionation, 17%, cage recombination, 20%, and cage escape, 63%.

Exploratory studies of the CpCo-mediated [2+2+2] cycloaddition of alkynes to the 2,3-double bond of benzo[b]furans (and some benzo[b]thiophenes) are presented, with the general aim to access morphinan substructures. The basic feasibility of constructing Co-complexed tetrahydrophenanthro[4,5-bcd]furans (and -thiophenes) in moderate to good yields is demonstrated, with complete to extensive diastereoselectivity. Limitations are the apparent necessity for bulky (silylated) monoalkynes, the lack of regioselectivity in the cocyclization with unsymmetrical alkynes, and the sensitivity of the ligands, both complexed and uncomplexed, with respect to ring opening and rearrangement.

nitriles nitriles (acyclic compounds) P 0350 -079Thermolysis of Acylazo O-Trimethylsilyl Cyanohydrins: Azoalkanes Yielding Captodatively Substituted Radicals. -Hitherto inaccessible azoalkanes (IV) and (VI), bearing geminal α-cyano and α-trimethylsiloxy groups, are prepared by a new synthetic method from acyl diazenes (II) and (V). The thermolysis kinetics and product studies of these two azoalkanes in the presence of thiophenol as hydrogen donor and with the TEMPO radical to scavenge the initially formed radicals is reported. The thermolysis rates do not support captodative radical stabilization. A 13 C-NMR product study of photolyzed compound (IV) in the presence of TEMPO at 21 • C shows that 17% of the caged radical pairs are disproportionated, 20% undergo cage recombination, and 63% cage escape.-(BILLERA, CHARLES F.; DUNN, TRAVIS B.; BARRY, DAVID A.; ENGEL, PAUL S.; J.