Density functional computations of alkynylation of nitrones catalyzed by chiral zinc(II)-complexes

The alkynylation of nitrones catalyzed by chiral zinc(II)-complexes was studied by means of the density functional theory (DFT). All the intermediates and transition states were optimized completely at B3LYP/6-31G(d,p) level. Calculation results confirm that this alkynylation of nitrones was endothermic and the total absorbed energy was about 14 kJ/mol. The formation of the M5 complexes was the rate-determining step and the chirality-limiting step for this alkynylation. The transition states TS3-re involve a H(8)–O(2)–Zn(6)–C(9)–C(14)–N(13)–O(12) 7-membered ring, and thus the transition states TS3-si involve a Zn(6)–C(9)–C(14)–N(13)–O(12) 5-membered ring. The dominant reaction is the attack of nitrones from the re-surface of M4. The reactivity of anti-nitrones was stronger than that of syn-nitrones for zinc-catalyzed alkynylation of nitrones. The dominant reaction channel was cata → TS1b → M1b → M2 → M3b → TS2b → M4b → TS3b1-anti-re → M5b1-anti-re → Pro-R. The dominant products predicted theoretically were of R-chirality, (2R)-N-hydroxy-N-methylpent-3-yn-2-amine. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.