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DOI: 10.1055/s-0030-1258756
Gold(I)-Catalyzed Synthesis of Furo[3,4-d]-[1,2]oxazines
Contributor(s):Victor Snieckus, Emilie DavidEast China Normal University, Shanghai and Shanghai Institute of Organic Chemistry, P. R. of China
Diastereo- and Enantioselective Gold(I)-Catalyzed Intermolecular Tandem Cyclization/[3+3] Cycloadditions of 2-(1-Alkynyl)-2-alken-1-ones with Nitrones
Angew. Chem. Int. Ed. 2010, 49: 6669-6672
Publication History
Publication Date:
21 October 2010 (online)
Key words
cycloaddition - nitrones - furo[3,4-d][1,2]-oxazines - gold
Significance
A previous regio- and diastereoselective tandem cyclization-[3+3] cycloaddition of 2-(1-allynyl)-2-alken-1-ones 1 with nitrones 2 lead to furo[3,4-d][1,2]oxazines 3 with moderate enantioselectivity using AuCl2 as catalyst and (R)-MeO-biphep as ligand (F. Liu, Y. Yu, J. Zhang Angew. Chem. Int. Ed. 2009, 48, 5505). In this report, the replacement of L3 by L1 (modification of the bite angle) or L2 (bulkier substituents on the phosphorous aryl moieties) allowed the synthesis of optically active furo[3,4-d][1,2]oxazines 3 in high yield and excellent diastereoselectivities. The choice of solvent was also crucial to keep high diastereoselectivity. The absolute configuration of products 3 was confirmed by single-crystal X-ray analysis.
Comment
Gold is a popular catalyst for the synthesis of a variety of heterocycles via intermolecular or intramolecular reactions (see Reviews below). This enantioselective transformation is the first one using Cn-tunephos/(AuCl2) for a gold-catalyzed reaction. It tolerates aromatic and cyclic ketones, but aliphatic substituents (R² and R³) gave lower enantio- and stereoselectivity, except with bulky groups like 1-cyclohexenyl. The N-O bond of products 3 can then be reductively cleaved affording tetrasubstituted amino alcohol containing furans without loss of ee via palladium-catalyzed hydrogenation.
Reviews: A. Arcadi Chem. Rev. 2008, 108, 3266-3325; N. T. Patil, Y. Yamamoto Chem. Rev. 2008, 108, 3395-3442.