The proline-derived N-sulfonylcarboxamide-catalyzed direct enantioselective alpha-oxidation of ketones and aldehydes with nitrosobenzene is presented. The reactions proceed smoothly furnishing the corresponding alpha-aminoxylated compounds in good yields with up to > 99% ee. The proline-derived N-sulfonylcarboxamides were also found to be excellent catalysts for the direct enantioselective nitroso Diels-Alder-type reaction between nitrosobenzene and of alpha,beta-unsaturated cyclic ketones yielding the corresponding bicyclic Diels-Alder adduct products with tip to > 99% ee. The proline-derived N-sulfonylcarboxamides represent a readily available and highly modular novel type of organic catalyst. (c) 2005 Elsevier Ltd. All rights reservesd.
Diastereo- and Enantioselective Synthesis of Nitroso Diels−Alder-Type Bicycloketones Using Dienamine: Mechanistic Insight into Sequential Nitroso Aldol/Michael Reaction and Application for Optically Pure 1-Amino-3,4-diol Synthesis
作者:Norie Momiyama、Yuhei Yamamoto、Hisashi Yamamoto
DOI:10.1021/ja066037m
日期:2007.2.1
This article presents complete diastereo- and highly enantioselective synthesis of nitroso Diels-Alder-type bicycloketones using dienamine. With the hydrogen bonding of two hydroxyls in the bulky binaphthol 1c, high enantioselectivities and complete diastereoselectivity are realized in 2-oxa-3-aza-bicycloketone synthesis. On the other hand, alpha,beta-unsaturated ketone can be employed as diene precursor, utilizing readily available tetrazole catalyst 3b, to provide the 3-oxa-2-aza-bicycloketones in moderate yields with complete enantioselectivities. Investigation into the reaction utilizing 2-morpholino-4,4-diphenylcyclohexadiene 2d clearly indicated that cyclization with the bulky binaphthol 1c is involved in the sequential process, the N-nitroso aldol reaction, followed by Michael addition. In addition, optically pure 1-amino-3,4-diol is synthesized from 2-oxa-3-aza-bicycloketones. Use of p-phenoxynitrosobenzene allows access to protected amino diol via cleavage of the N-Ph bond.
A Highly Active 4-Siloxyproline Catalyst for Asymmetric Synthesis
trans-4-tert-Butyldimethylsiloxy-L-proline displays a greater catalytic activity than the parent proline without compromising the enantioselectivity, which widens the substrate scope in the α-aminoxylation of carbonyl compounds, as well as O-nitroso-aldol/Michael, and Mannich reactions.