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Model studies of the reduction of 3‐phenyl‐6 H ‐1,2‐oxazines, chemo‐ and stereoselectivity: synthesis of amino alcohols, amino acids, and related compounds
Author(s) -
Zimmer Reinhold,
Hoffmann Matthias,
Reißig HansUlrich
Publication year - 1992
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19921251012
Subject(s) - chemistry , raney nickel , stereoselectivity , pyrrolidine , medicinal chemistry , chemoselectivity , acetic acid , organic chemistry , pyrrole , catalysis , yield (engineering) , materials science , metallurgy
Abstract While palladium‐catalyzed hydrogenation of 3‐phenyl‐6 H ‐1,2‐oxazine 1 produces primary amine 5 in a nitrogen‐transposition reaction, the reductions of the related 1,2‐oxazines 2, 10 , and the 1,2‐oxazin‐6‐one 3 afford the expected amino alcohols 4, 11 , and the γ‐amino acid 6 , respectively, with low diastereoselectivites. In the presence of acetic acid 3 is reductively converted into γ‐keto carboxylic acid 9 and 1 into the γ‐lactam derivative 12 probably by a ring contraction to a nitrone intermediate. Raney nickel as the catalyst is able to transform 1,2‐oxazine 7 bearing an exo‐methylene unit into 3,4‐dihydro‐2 H ‐pyrrole 13 . The reaction of 6 H ‐1,2‐oxazine 1 with aluminium amalgam produces pyrrole 14 in moderate yield. Treatment of 1 with sodium in 2‐propanol brings about its transformation into pyrrolidine derivative 15 together with pyrrole 14 and amino alcohol 4 as minor products. The chemoselectivity and stereoselectivity of these reductions are discussed including mechanistic proposals for the multistep processes involved.