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Amines and amides MICHAEL NORTH Department of Chemistly, University of Wales, Bangol; Gwynedd, UK LL57 2W Reviewing the literature published in 1996. Continuing the coverage in Corztemporaly Organic Synthesis, 1996, 3, 323. 1 2 2.1 2.2 2.3 2.3.1 2.3.2 2.3.2.1 2.3.2.2 2.3.3 2.3.3.1 2.3.3.2 2.3.4 3 3.1 3.2 3.2.1 3.3 4 5 Introduction, scope and coverage Preparation of amines Synthesis of achiral or racemic amines Synthesis of optically active amines Synthesis of amines bearing additional functional groups Synthetic routes to P-hydroxyamines Synthesis of a-amino acids Synthesis of racemic and achiral %-amino acids Asymmetric syntheses of a-amino acids Synthesis of /)-amino acids Racemic syntheses of P-amino acids Asymmetric syntheses of p-amino acids Synthesis of y- and higher amino acids Preparation of amides General methods, and the synthesis of acyclic amides Synthesis of lactams Synthesis of p-lactams Synthesis of peptides Summary References 1 Introduction, scope and coverage This review covers the literature published during 1996. References were obtained in the same way as in previous years, and the review has the same format as that used last year.' During the last twelve months, there has been an explosion of publications dealing with the related fields of solid supported synthesis and combinatorial synthesis. Most of these papers deal with the application of well developed solution phase methodology to solid state reactions, and this area has been extensively reviewed during 1996,*-' including a whole issue of Accounts of Chemical Research. In view of this, and to keep this report to a reasonable length, papers dealing just with solid phase or combinatorial synthesis have been omitted from this year's review unless they are of special importance, and the interested reader is referred to the reviews cited above. 2 Preparation of amines 2.1 Synthesis of achiral or racemic amines A large number of reducing agents can be used during a reductive amination procedure to produce secondary amines, with sodium cyanoborohydride being the most common. However, the use of magnesium metal in methanol buffered with acetic acid and triethylamine has now been recommended. The reducing system is highly selective and produces no tertiary amines or alcohols as impurities.6 The addition of allylic barium reagents to imines occurs with allylic rearrangement at -78 "C, whilst at 0 "C no allylic rearrangement occurs. It was shown that the former reaction occurs under kinetic control, whilst the latter gives the thermodynamically more stable product. The reaction was also extended to chiral imines, with asymmetric induction being observed in both cases, though the low temperature reaction gave the better diastereomeric exce~s.~ Sibutramine 1 is a potential drug for the treat- ment of obesity, and a synthesis of 1 along with a number of its metabolites has been reported. The synthesis starts from 4-chlorophenylacetonitrile which is first converted into cyclobutane 2, sub- sequent addition of iso-butylmagnesium bromide to the nitrile, hydrolysis, reductive amination and
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