A New Protocol for the In Situ Generation of Aromatic, Heteroaromatic, and Unsaturated Diazo Compounds and Its Application in Catalytic and Asymmetric Epoxidation of Carbonyl Compounds. Extensive Studies To Map Out Scope and Limitations, and Rationalization of Diastereo- and Enantioselectivities
作者:Varinder K. Aggarwal、Emma Alonso、Imhyuck Bae、George Hynd、Kevin M. Lydon、Matthew J. Palmer、Mamta Patel、Marina Porcelloni、Jeffery Richardson、Rachel A. Stenson、John R. Studley、Jean-Luc Vasse、Caroline L. Winn
DOI:10.1021/ja034606+
日期:2003.9.1
a general process for the in situ generation of diazo compounds from tosylhydrazone sodium salts has been established and applied in sulfur-ylide mediated epoxidation reactions. The chiral, camphor-derived, [2.2.1] bicyclic sulfide 7 was employed (at 5-20 mol % loading) to render the above processes asymmetric with a range of carbonyl compounds and tosylhydrazone sodium salts. Benzaldehyde tosylhydrazone
absolute stereochemistry has been achieved by generating the reactive intermediate (the diazo compound) in situ from tosylhydrazone salts (see scheme, PTC=phase-transfer catalyst, Ts=toluene-4-sulfonyl). High yields (58-82 %), high d.r. (88:12-98:2), and high ee values (87-94 %) have been obtained using a new class of stable chiral sulfides at low catalyst loading (5 mol %) and [Rh2 (OAc)4 ] (0.5 mol %).