Primary and N -secondary 2-phosphanylanilines were synthesized via metallation of 2-bromoanilines, coupling with ClP(NMe 2 ) 2 , alcoholysis and reduction with LiAlH 4 , and subsequently reacted with formimidoester hydrochloride to give 1,3-benzazaphospholes. For 1 H -1,3-benzazaphospholes, a shorter alternative three-step synthesis was developed, based on N -acylation of 2-bromoaniline, NiCl 2 -catalyzed arylation of triethyl phosphite and a new reductive cyclization of amidophosphonic acid ester with excess LiAlH 4 .The complex chemistry of phospholes and phosphole anions has found considerable interest in recent years. 1,2 Little is known, however, about metal derivatives or complexes of related 1,3-azaphospholes 3 or annulated azaphospholes. 4Ð7 The early papers presented an interesting ambident reactivity of the Ò N Ó-lithiated and the first stable RP=C(Li)-X species, but since then no further work on these compounds has been reported. 8 One of the reasons may be the cumbersome synthetic access of azaphospholes 8 and benzazaphospholes 4,5 by multi-step procedures. We describe here in more detail the organometallic route 5 and a new and shorter way to prepare 1 H -1,3-benzazaphospholes. The original synthesis of 1 H -1,3-benzazaphospholes was based on cyclocondensations of various carbonic acid derivatives with 2-phosphanylanilines. The latter were prepared by photoinitiated MichaelisÐBecker reaction of sodium diethyl phosphite with 2-iodoaniline in liquid ammonia and subsequent reduction with LiAlH 4 . 9 For further studies of benzazaphospholes, we explored a preliminary reported organometallic route 5 with respect to a more general use in the synthesis of 2-phosphanylanilines. 2-Bromoaniline (1) was reacted successively with three equivalents of butyllithium, phosphorous acid bis(dimethylamide) chloride and ethyl alcohol in a one-pot reaction. After removal of volatile components (bath temperatutre 100¡C/0.01 Torr), the resulting mixture was reduced with excess LiAlH 4 to give 2-phosphanylaniline 2 in a total yield of 30% (Scheme 1). Small impurities of secondary phosphanes could not be removed by distillation but did not interfere with the further reaction of 2 with formimidoester hydrochloride affording the non-basic 1 H -1,3-benzazaphosphole 3 , which can easily be purified.
Scheme 1For N -substituted derivatives, the following reaction sequence was established. 2-Bromo-N -acylanilides 4 , obtained from 1 ,were reduced with LiAlH 4 to give N -alkyl-2-bromoanilines 5 . The latter were dilithiated and reacted with ClP(NMe 2 ) 2 to give 6 which were converted to 7 with ethanol. Then 7 was reduced to 8 with LiAlH 4 and the latter underwent cyclocondensation with formimidoester hydrochloride affording the N -alkyl-1,3-benzazaphospholes 9 (Scheme 2). Shortcomings of these procedures were low yields in the substitution of the tri-or dilithium compounds if the reactions were carried out on a larger scale.
Scheme 2A further disadvantage is the easy replacement of bromine by hydrogen during the reduction of 4 with...
