Benzazaphospholes

A-Unsubstituted 1,2,3-benzazadiphospholes (179) (R, R = H, Me, Cl) are yellow solids and result from a synthesis analogous to that used for 1,3-benzazaphospholes (chapter 3.16) as yellow solids <90TL4463, 93PS(76)45>. They are converted to the anions by a strong base. 1,3-Dienes such as 2,3-dimethylbutadiene give a [2 -I- 4] cycloaddition to the P=P bond <90TL4463>. 

In the case of phenyl isocyanide, both the addition of f-BuLi and an ortho lithiation took place in the presence of TMEDA to provide the intermediate 53 and finally compounds 54 and 55 (Scheme 15)75. The corresponding 3-metalloindolines (metal = S, P, Si, Ge, Sn) were obtained by reaction of the dilithium intermediate 53 with metal dihalides. The obtained benzazaphospholes and benzazarsoles 54 (M = f-BuP, MeAs) can be converted into the aromatic III-1,3-benzazaphospholes and benzazarsoles 55 by flash vacuum pyrolysis76. 

Complexes of 1,3-benzazaphosphole systems with other metal carbonyl compounds (Cr, Mo, as well as W) also follow the same pattern, reaction at phosphorus <1998EJI1079>, and exactly comparable behavior was seen in the formation of complexes 61 and 62 from dihydrothiazole-fused and dihydrooxazole-fused 1,3-azaphospholes, respectively <1999JOM(577)337>. 

C-Lithiation (to give 71) of the 1,3-benzazaphospholes 70 was achieved with /-BuLi and the C-lithiated reagents proved to be synthetically very useful, reacting with a variety of electrophiles to produce 2-substituted derivatives 72 as indicated in Scheme 8 < 20020M912>. 

Reduction of o/t/ ti-acylaminoaryl phosphonic acid esters 94 with LiAlH4 produced 1,3-benzazaphospholes 95 (Scheme 15) <2001T9963, 2002JOM(646)113>. 

Heterophospholes were introduced in Chapter 3.15.1. The first fully unsaturated phospholes with a nonadjacent second heteroatom were 1,3-benzazaphospholes (1). They were first described in 1978 <78TL44i> and were consequently mentioned in the first edition of Comprehensive Heterocyclic Chemistry (CHEC-I) <84CHEC-l(l)523>, together with 1,3-benzothiaphospholes (2) and 1,3-benzodiphospholes (3) <80TL3483>. 1,3-Benzazarsoles (4) were also first studied at that time <78JOM(154)l>. 

UV and PE spectra of 3-alkyl 1,3-benzazaphospholes and 1,3-benzazarsoles are consequently completely different from those of their lif-isomers <94M1 316-0l>. 

In contrast to most of the azaphospholes with more than the two heteroatoms (which are covered in Chapter 4.22) 1,3 azaphospholes/arsoles and 1,3-benzazaphospholes/arsoles are not (or only slowly) attacked by water, dilute acids or bases, alcohols and amines. Concentrated acetic acid reconverts (1) to 2-aminophenylphosphine. 

A-Unsubstituted 1,3-benzazaphospholes and 1-methyl 1,3-benzazaphospholes are not basic and are not extracted from an organic phase by dilute sulfuric acid. They do not react with methyl iodide but are F/ -alkylated by Me30 BF4 <83JOM(258)257, 94MI 3i6-oi>. A P-Cr CO)i complex of 2-phenyl 1,3-benzazaphosphole is known <81ZAAC(481)22>. 

Azaphospholes/arsoles and 1,3-benzazaphospholes/arsoles neither add hard nucleophiles (as mentioned above) nor soft nucleophiles such as PhSH or PhAsH2. Exceptions are MejSnH which adds to the As=C bond of l,2-dimethyl-l,3-benzazarsole on heating to 130°C <94Ml 316-01 >, and LiBu as described above. 

Like 1-methyl-1,3-benzazaphospholes/arsoles, the 1,3-benzoxaphospholes/arsoles (38) are unre-active to water, alcohols or amines. However, in contrast to them they add HCl, PhSH, and PhAsH2, and in the presence of AIBN they also add McjSnH. In this reaction (38a) is always less reactive than (38b) PhMePH only adds to (38b). Adducts (40) undergo a dismutation to yield the dihydro derivatives (41). (41) also results from (38a) and McsSnH. 

The reactivities of 1,3-benzazaphospholes (1) and 1,3-benzodiphospholes (3) as well as those of their anions have been compared <91PS(56)I89>. 

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