Azaphospholes 1.2.4- Diazaphospholes

Carbon-phosphorus double bonds are also formed in addition reactions of tris(trimethylsilyl)phosphine 1692 (which can be readily prepared from white phosphorus, sodium, and TCS 14 [13a,b,c]) to give oxazohum fluorides 1691 which then give the azaphospholes 1694, via 1693 [3, 14]. On addition of 1692 to 1695, the diazaphosphole 1696 [3, 15] is prepared, whereas l,3-azaphospholo[l,2a]pyridines 1698 [16] are formed from 1692 and 1697, and 1,3-thiaphospholes 1700 are formed from the dithiohum fluorides 1699 [17]. l,3-Benzodiphospholyl anions 1703 are generated by reaction of acid chlorides with the dihthium salts 1701, via 1702 [18] (Scheme 11.3). 

Monocyclic 2H-[ 1,2,3 Idiazaphospholes (B) are easily accessible from the condensation of the four-membered chain incorporated in hydrazones or azoalkanes with phosphorus trichloride making available a large number of representatives that have been intensively studied [2, 4, 7], In contrast, their 1//-isomers (A) are less known and are obtained only as second minor product during the synthesis of 2//-[l,2,3]diazaphospholes in some cases. A facile synthesis for pyrido-anellated azaphospholes has been developed in our group by making use of 1,2-disubstituted pyridinium salts for condensation with phosphorus trichloride [8, 13-15], Accordingly, cyclocondensation of 2-alkyl-1-aminopyridinium iodides (1) with phosphorus trichloride in the presence of triethylamine affords pyrido-anellated l//-[l,2,3]diazaphospholes, i.e. l,2,3]diazaphospholo 1,5-a] pyridines (2) (Scheme 1) [16],... 

Planarization of the P-substituted azaphospholes results in structures with similar aromaticity to the planar phosphole. Replacement of the CH units by N in these rings has some effect on the barrier to planarization. The MP2/6-31C(d) barrier of 277-1,3,2-diazaphosphole was 17.6, while that of 377-1,5,3-diazaphosphole was 13.5 kcal/mol (phosphole 17.2 kcal/mol at the same level). ... 

A 1978 review (78S557) covers heterocycles containing a PNN-linkage and includes 1,2,3-diazaphospholes and 1,2,3,4-triazaphospholes. Azaphospholes and, more general, heterophospholes... 

The 177-1,2-azaphospholes are colorless to yellow solids or oils and are stable at ambient temperature <20008417, 1998ICA(270)273, 2003ZNB44>. Most of the reactions reported so far involve the dicoordinated phosphorus atom, which represents the reactive center of the molecule. l,3-Di(fet/-butyl)-5-phenyl-177-l,2-diazaphosphole reacts under mild conditions with alkyl triflates CF38O3R (R = Me, Et) to afford the P-alkylated 1,2-azaphospholium compounds la and lb in quantitative yields. With an equimolar amount of iron nonacarbonyl, the Tj -complex 2 was selectively formed in 63% yield (Scheme 1) <2002EJ01664>. 

Dicyano-l,3,2-diazaphospholes (6 R = Me, TMS) are converted to 5-cyano-l,2-azaphos-phospholes (l,2-azaphosphole-5-carbonitriles) (7) by reaction with alkynes —R, ... 

The electronic structure and degree of aromaticity of 1,3-azaphospholes has received attention from the theoreticians. An alternative synthesis of the phospha-indolizine system (201), from the reaction of pyridinium salts with phosphorus trichloride, has undergone further development " and has also been applied in the synthesis of fused 1,4,2-diazaphospholes, e.g., (234) ", 2 (235). The 1,2,4,3-triazaphosphole system (236) has been isolated as an... 

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