2-Amino-4H-pyrans are an important group of compounds with various applications.Some have been shown to exhibit biological activity and have been used as anti-cancer,antihypertensive and coronary dilating agents.1'3 They are also important intermediates in organic synthesis.4"9 A number of different methods for the synthesis of 2-amino-4H-pyran derivatives have been described.We now report a one-pot synthesis of dimethyl,diethyl and di-tert-butyl-2-(tert-butylamino)-5-benzoyl-6-phenyl-4H-pyran-3,4-dicarboxylate(5a-c)and of dimethyl,diethyl,di-tert-butyl-2-(cyclohexylamino)-5-benzoyl-6-phenyl-4H-pyran-3,4-dicar-boxylates(5d-f)in fairly high yields.One of us has already reported the reaction between alkyl isocyanides(1)and dialkyl acetylenedicarboxylates(2)in the presence of 1,3-diphenylpropane-1,3-dione to afford the highly functionalized ketenimines 3.17 Reflux of these ketenimines in benzene for 2-3 days led only enolization to compounds 4 without cyclization.By changing the addition sequence of the reactants and using the suitable base,we have achieved the preparation of 2-amino-4H-pyrans(5a-f)in good yields(Scheme 1).
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