Trichloropyruvate N-acylimines. Reactions with phosphorus nucleophiles

Abstract

Reactions of N-aroyltrichloroethaneimines CCl 3 C(R)=NCOAr (II, R = COOMe, CN) with phosphorus nucleophiles were studied. The reaction of imines II with o-phenylenediethylamidophosphite proceeded as [4+1]-cycloaddition leading to formation of stable spirocyclic phosphoranes. The structure of one of them was proved by the XRD analysis. The reaction of imine II with acyclic P(III) derivatives [Ph 3 P, Ph 2 POEt, (PhO) 3 P] also includes the formation of labile monocyclic phosphoranes which eliminate phosphine oxide and undergo chlorotropic transfer leading to trichloroazadienes CCl 2 =C(R)N=C(Cl)Ar. The reaction of imines II with (EtO) 2 POH in the presence of triethylamine leads to the formation of (EtO) 2 P(O)Cl and the corresponding dichlorovinylamides CCl 2 =C(R)NHCOAr.N-Acylamines are valuable highly reactive building blocks in the synthesis of various nitrogen-containing compounds [1][2][3][4]. Activated imines with the carboxyl group at the imine carbon atom are of special interest because their functionalization leads to derivatives of α-amino acids exhibiting high biological activity. For example, trifluoropyruvate N-acylamines easily react with nucleophilic and dipolar reagents to form biologically important derivatives of trifluoroalanine [3,[5][6][7]. At the same time imines of trichloropyruvates until recently were not practically studied because preparative methods of their synthesis were lacking. We have developed lately a convenient method for the preparation of trichlotopyruvate N-acylimines from dichlorovinylamides I (Scheme 1) [8]. It was shown that these substances easily react with S-,O-,N-, and Cnucleophiles to form functional derivatives of α-amino acids containing trichloroalanine fragment. It turned out that this method was sufficiently universal and was suitable for the synthesis of previously unknown nitriles of acyliminotrichloropropanoic acids II (R = C≡N). In the work the synthesis is described of the first representative of such compounds IIc and the reactions of phosphorus nucleophiles with N-aroylimines containing methoxycarbonyl (IIa, IIb) or nitrile group at the imine carbon atom.Analysis of published data shows the variety of pathways taken by the reaction of N-acyl-α-haloalkaneimines with nucleophilic phosphorus derivatives [9]. In particular, haloalkane acylimines can react with the participation of the C=N bond, of haloalkyl fragment, or heterodiene system C=N-C=O to give the products of C-and/or N-phosphorylation which in their turn often undergo further transformations [9]. The direction of these reactions is very sensitive to the nature of substituents at the azomethine bond, the nature of phosphorus reagent, and halogen in the haloalkyl fragment. For iminocarboxylates IIa, IIb and