Cyclic oxonitriles: stereodivergent grignard addition-alkylations

Sequential carbonyl addition-conjugate addition of Grignard reagents to cyclic 5-7-membered oxoalkenenitriles efficiently generates cyclic magnesiated nitriles. Alkylations of these magnesiated nitriles exhibit diastereoselectivities that depend intimately on the size of the carbocyclic ring: 5-membered oxonitriles generate magnesiated nitriles whose alkylations are controlled by steric constraints whereas 6- and 7-membered oxonitriles generate internally coordinated, C-magnesiated nitriles whose alkylations are controlled by stereoelectronic effects. Reversing the alkylation selectivity of 6-membered C-magnesiated nitriles is achieved by conversion to an N-metalated nitrile in which steric, rather than electronic, effects direct the electrophile trajectory. Collectively, the conjugate addition-alkylation generates highly substituted, cyclic 5-7-membered nitriles containing three new stereocenters with selective access to diastereomers at the quaternary nitrile-bearing carbon.

Unsaturated Nitriles: Precursors for a Domino Ozonolysis-Aldol Synthesis of Oxonitriles

Cyclic five-, six-, and seven-membered oxonitriles are prepared by a tandem ozonolysis-aldol sequence. Cyclopentenylacetonitrile (4) and cyclohexenylacetonitrile (12) afford the ring-expanded oxonitriles 3 (98%) and 17 (58%), respectively, in highly efficient one-pot syntheses. Homologous five-membered oxonitriles 22a-c are prepared by analogous ozonolysis-aldol cyclizations employing omega-alkenyl beta-ketonitriles. The method tolerates various substitution patterns and allows for the synthesis of beta,beta-disubstituted oxonitriles (22c). The reaction conditions are essentially neutral providing the beta-hydroxyoxonitriles 22d and 22e with only trace amounts of the aromatic dehydration product.