3- azaphospholes

Benzonitrile with [( -Cp )P W(CO)5 2] gives 82, the result of migration of the phosphorus atom, insertion of the nitrile moiety into the P-C bond and further C-H bond activation (01AGE3413). 

2-azaphosphole /7 P)-coordinated complexes 83 and 84 follow from the corresponding ligand and [(/7 -allyl)NiCl]2 and [(1,5,9-cyclododecatriene)Ni], respectively (98ICA(270)273). 

2-phosphaindolizine 94 that follows from the ligand and [(THF)Cr(CO)5j (98EJIC1079). 

---

Four-membered heterocycles are easily formed via [2-I-2] cycloaddition reac tions [65] These cycloaddmon reactions normally represent multistep processes with dipolar or biradical intermediates The fact that heterocumulenes, like isocyanates, react with electron-deficient C=X systems is well-known [116] Via this route, (1 lactones are formed on addition of ketene derivatives to hexafluoroacetone [117, 118] The presence of a trifluoromethyl group adjacent to the C=N bond in quinoxalines, 1,4-benzoxazin-2-ones, l,2,4-triazm-5-ones, and l,2,4-tnazin-3,5-diones accelerates [2-I-2] photocycloaddition processes with ketenes and allenes [106] to yield the corresponding azetidine derivatives Starting from olefins, fluonnaied oxetanes are formed thermally and photochemically [119, 120] The reaction of 5//-l,2-azaphospholes with fluonnated ketones leads to [2-i-2j cycloadducts [121] (equation 27)... 

Azaphospholes and especially di-, fri- and penfaphospholyl sysfems offer a wide variefy of coordinafion modes fhaf frequenfly cannof be found in... 

Azaphospholes where heteroaromaticity is regarded as appreciable, however, act mainly as (P) ligands, and often the P-donor carries two coordinated organometallic moieties. 

Regitz has shown that the reaction of azaphosphole 38 with two equivalents of DEAD furnishes the zwitterionic 2 1 adduct 39 (Scheme 8) [52]. The extreme low frequency shift of the P NMR signal by more than 220 ppm in comparison to that of the azaphosphole confirms the formation of a betaine possessing a hexacoordinated phosphorus atom. 

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). 

A solution of 5 mmol diazomethane, prepared from N-methyl-N-nitrosourea (0.62 g, 6 mmol), in 5 mL pentane is added to 1728 a (0.5 g, 5 mmol) [4] at 0°C and the reaction mixture warmed to room temperature. After 30 min the yellow color of CH2N2 has disappeared and the reaction mixture is evaporated. The residue is extracted with boiling pentane to give 0.66 g (93%) 3-tert-butyl-lH-l,2,4-di-azaphosphol, m.p. 74°C [30] (Scheme 11.10). 

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],... 

The reaction of azaphosphole 232 with 2 equiv of DEAD gives ths zwitterionic spiroperphosphoranide 233 in 37% yield (Equation 49) <2000S417>. 

Scheme 50 1H-1,2-Azaphospholes via carbovanadation of alkynes with 1 -aza-2-phospha-4-vanada-2-cyclobutanes.

A potentially useful synthesis of 177-1,2-azaphospholes by the reaction of alkynes with l-aza-2-phospha-4-vanada-2-cyclobutenes generated from R1N=VC13 and phosphaalkynes may be considered as an example of cyclic carbovanadation 4 (Scheme 50). 

---