Computer-Assisted Design of Asymmetric 1,3-dipolar Cycloadditions between Dimethylvinylborane and Chiral Nitrones

JESÚS DÍAZ; MARÍA A. SILVA; JONATHAN M. GOODMAN; SILVINA C. PELLEGRINET

TETRAHEDRON

Elsevier

Año: 2005 vol. 61 p. 10886 - 10893

0040-4020

This report describes a theoretical study of the 1,3-dipolar cycloadditions between dimethylvinylborane and different chiral nitrones aimed at identifying the requisite structural features to achieve high levels of selectivity. Excellent regioselectivities towards the formation of the 5-borylisoxazolidines are computed in all cases due to the presence of a strong secondary orbital interaction between the boron of the vinylborane and the oxygen of the nitrones. While these transition structures show [3 + 3] character, 4-boryl regioisomeric structures have classical [3 + 2] character with weak carbon-boron secondary orbital interactions. Endo transition structures leading to the favored products adopt chair-like conformations only, unlike their exo counterparts which exhibit either boat or twist-boat structures. Placing a stereocenter adjacent to the nitrone nitrogen appears to be an effective strategy to stereodiscriminate the anti and syn approaches of the dipolarophile.