Benzo diazaphosphole

Diazaphospholes 6 are colorless to pale yellow distillable liquids or crystalline solids that are stable to oxidation by air and do not react with elemental sulfur. 1,3,2-Oxazaphospholes 8 and 1,3,2-thiazaphospholes 9 are mainly known as benzo and fused derivatives. In CHEC-II(1996), only the chemistry of 4,5-dicyano-l,3,2-diazaphosphole, 1,3,2-benzo-diazaphospholes, 1,3,2-benzoxazaphospholes, and 1,3,2-benzothiazaphospholes is discussed <1996CHEC-II(4)771>. No significant new results on the chemistry of 1,3,2-oxaza- and 1,3,2-thiazaphospholes have been reported since the publication of CHEC-II(1996). 

Benzannulated NHPs are straightforwardly accessible from AUV-disubsti luted o-phenylenediamines either via base-induced condensation with substituted dichlorophosphines [25] or PC13 [26], or via transamination with tris(dialkylamino) phosphines [13, 14, 27], respectively. An analogous NH-substituted derivative was obtained in low yield via transamination of o-phcnylcncdiaminc with ethoxy-bis(diethylamino)phosphine [28], and condensation of o-phenylenediamine with excess tris(diethylamino)phosphine furnished a l,3-bis(phosphino)-substituted heterocycle [29], Intermediates with one or two NH functions were detectable by spectroscopy but could not be isolated in pure form under these conditions. However, 2-chloro-benzo-l,3,2-diazaphospholene and the corresponding 1-phenyl derivative were prepared in acceptable yield via condensation of PC13 with o-phenylenediamine under microwave irradiation [30], or with A-phenyl-o-phenylenediamine under reflux [27], respectively, in the absence of additional base. The formation of tetrameric benzo-NHPs during transamination of A-alkyl-o-phenylenediamines with P(NMe2)3 has already been mentioned (cf. the section entitled 1,3,2-Diazaphospholes and 1,3,2-Diazaphospholides ). 

Transformations through 1,2-addition to a formal PN double bond within the delocalized rc-electron system have been reported for the benzo-l,3,2-diazaphospholes 5 which are readily produced by thermally induced depolymerization of tetramers 6 [13] (Scheme 2). The monomers react further with mono- or difunctional acyl chlorides to give 2-chloro-l,3,2-diazaphospholenes with exocyclic amide functionalities at one nitrogen atom [34], Similar reactions of 6 with methyl triflate were found to proceed even at room temperature to give l-methyl-3-alkyl-benzo-l,3,2-diazaphospholenium triflates [35, 36], The reported butyl halide elimination from NHP precursor 13 to generate 1,3,2-diazaphosphole 14 upon heating to 250°C and the subsequent amine addition to furnish 15 (Scheme 5) illustrates another example of the reversibility of addition-elimination reactions [37],... 

During the last 10-15 years, more emphasis has been on the development of new synthetic routes for obtaining variously substituted less common representatives and new varieties of CC- or C/V-anellated bicyclic diazaphosphole systems. CC-Anellation is possible in A, B, and D, out of which benzo anellated representative of only D has been reported. But, C7V-fused derivative of D is not reported, though... 

Previous attempts to synthesize benzo[l,3,2]diazaphosphole (59) in an analogous manner from benzene- 1,2-diimines by Malavaud et al. led to tetra-meric cyclo-phosphazanes, which existed in equilibrium with monomer only at... 

Likewise, thiazolol3,2-<7 1,4,2 diazaphospholes and their 5,6-dihydro and benzo derivatives (87) reacted with 2,3-dimethylbutadiene and with isoprene with or without sulfur/selenium to give [2+4] cycloadducts 88 and 88 diastereo- and regioselectively (Scheme 27) [100],... 

Likewise, we obtained [l,4,2]diazaphospholes anellated to pyridines (13) [27], thiazoles (15) and their 5,6-dihydro- (16) and benzo- (17) derivatives [28, 29] from the condensation of l-alkyl-2-aminocycloiminium salts with PC13 in the presence of Et3N (Scheme 3). 

The 3-substituted 2-aminothiazolium bromides undergo cyclocondensation with phosphorus trichloride in the presence of triethylamine to give 3-substituted thiazolo[3,2-i/][l,4,2]diazaphospholes (271), the 5,6-dihydro and the benzo derivatives (Equation (74)) <92S267>. 

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