1.2.4- Diazaphospholes, 3,5-disubstituted

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],... 

On the other hand, 3,5-disubstituted [l,2,4]diazaphosphole 29 could be obtained from the reaction of tri-ferf-butylphenylphosphaethyne (25) with freshly prepared lithiated trimethylsilyldiazomethane (30) and subsequent treatment of the initially formed diazaphospholide ion (31) with trifluoroacetic acid (Scheme 9) [33],... 

Zheng et al. treated potassium [l,2,4]diazaphospholides, obtained from the reaction of 3,5-disubstituted-[l,2,4]diazaphospholes with metallic potassium in THF, with [Cp RuCl]4 to afford [(T75-dp)RuCp ] type pseudoruthenocene complex (106) (Scheme 33). Sandwich structure with almost eclipsed orientation of two n-bonded ligands has been confirmed by X-ray crystal structure determination [110], Catalytic application of [(rf-dp)RuCp ] complexes in the Heck reaction has also been investigated [111]. 

No reaction occurs with methyl iodide however, on reacting with Me2S04, [1,4,2] diazaphospholo[4,5-a]pyridines [27] and 11,2,3 diazaphospholo[4,5-a -pyridincs [34] furnish a2-A-methylated salts. Similar behaviour is shown by thiazolol 3,2-<7 [l,4,2]diazaphospholes [28], However, 1,3-benzazaphospholes are alkylated at phosphorus. This allows the access to N,P-disubstituted benzazaphospholium salts, potential precursors to heterocyclic 1,3-aminophosphinocarbenes [47],... 

The 2-X. -phosphaquinolines (117) were surprisingly the products when a phosphinidyne-ammonium salt (118) and an alkyne were stirred together in toluene, followed by addition of a base a mechanism via a phosphirene as shown was given. Attempts to prepare 4,5-disubstituted 1,2,4,3-triazaphospholes from amidrazones (119) and tris(dimethylamino)phosphine gave tetramers (120) monomeric boron trifluoride complexes (121), however, could be obtained. Several condensed 1,4,2-diazaphospholes (122) and (123) have been prepared. 

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