On the nature of intermediates in the reactions of carbanions of diethyl arylmalonates with isocyanates

Abstract

A reaction of ethyl phenyl and 4 nitrophenylmalonate carbanions with para tolylsulfonyl isocyanate leads to stable addition products, the corresponding substituted para tolyl sulfonylacylamides.Key words: ethyl phenyl and 4 nitrophenylmalonate carbanions, para tolylsulfonyl iso cyanate, para tolylsulfonylacylamides.During consideration of mechanism for the formation of carbamates by the reaction of isocyanates with carban ions 1 based on phosphorus containing zwitterions, 1,2 phenylcyanacetic esters, 3 and pyridinium ylides 4 , it was suggested that N anion 2 is formed as an intermediate (Scheme 1). The formation of the intermediate 2 was confirmed by the data of quantum chemical calculations for the reaction of pyridinium ylide, malonic ester deriva tive, with phenyl isocyanate. 4 At the same time, experi ments using 1 H NMR spectroscopy and kinetic data 2 did not show formation of intermediate 2 as kinetically stable species on the reaction coordinate.To answer the question whether the intermediate N anion 2 is formed in the transformations under study, Scheme 1 R = Ph; Py (+) ; ; R´3P (+) CH 2 , R´ = Pr n , Pr i , Bu n , Et 2 N; X = O, S; Alk = Me, Et, allyl, CH≡CCH 2 ; R″ = Me, cyclo C 6 H 11 , Ar.we considered a model reaction of carbanions 5a,b with tosyl isocyanate (Scheme 2). We presumed that if the reactions with aryl isocyanates proceed according to Scheme 1 through the formation of N anions 2, then the analogous reaction with tosyl isocyanate according to Scheme 2 will lead in the first step to the stable intermedi ate 6, the nucleophilicity of which should be extremely low due to the strong electron withdrawing power of the tosyl group. Scheme 2 R = R´ = H (a); R = NO 2 , R´ = H (b). Ts = SO 2 C 6 H 4 Me pIn fact, the reaction of tosyl isocyanate with carban ions obtained in the solution of THF from CH acid 5a,b and NaH proceeds at room temperature and, after acidifi

Formation of carbamates by reaction between ester carbanions and isocyanates: General regularities and scope

“…Unlike multiple proton signals in NMR spectra of carbamates obtained from phenyldiethylmalonate and arylisocyanates 13, signals of protons of ethoxycarbonilic groups in amides 15a and 15b were represented by a single group. Major results of x-ray analysis of tosylamide 15a have been published in a brief communication [17]. Results of x-ray analysis of 15b can be summarized as follows: According to the x-ray diffraction data, the replacement of a hydrogen atom in para-position of a phenyl ring with a nitro group (15b) does not cause deviation of the bond lengths from the expected values (Fig.…”