2-Trimethylsilyl- 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). 

Use of tris(trimethylsilyl)phosphine as the phosphorus furnishing reagent in condensation reaction with a-diazocarboxylic chlorides (7) gave 2-trimethylsilyl-[l,2,3]diazaphospholes (9) in good yields (Scheme 3) [18],... 

More recently, [2+3] cycloaddition reaction of the tri-te/t-butylphenylphosphaethyne (25) has been reinvestigated, when in spite of the steric encumbrance of extremely bulky Mes group, the use of trimethylsilylated diazomethane (24) makes its cycloaddition successful, which is followed by SiMe3/H migration yielding bulky [l,2,4]diazaphospholes [33], Phosphaalkyne 25 reacts with 24 in a regioselective manner to form intermediate cycloadduct 26, which undergoes facile aromatization... 

Exocyclic phosphorus of aminophosphinodiazaphosphole 122 on oxidation with trimethylsilyl azide gave (((trimethylsilyl)imino)phosphorano)diazaphosphole (124) the latter by transmetalation reaction with Cp TiCl3 at elevated temperatures yielded titanium iminophosphorane 125 (Scheme 36) [83],... 

A further example of the diazaphosphole synthesis by [3 + 2] cycloaddition is given by the reaction of a phosphoranediyl diazomethane (26) (R = NPr j) with P-chloro-bis(trimethylsilyl)-phosphaethene. The adduct loses trimethylchlorosilane and yields a 3-phosphoranediyl-l,2,4-diazaphosphole (or 3-phosphonio-l,2,4-diazaphospholide) (27). The analogous addition to the trimethylsilyl substituted P-chloro-bis(methylene)phosphorane (28) yields a 4-methylene derivative (29) of this diazaphosphole (molecular structure in Table 1). It provides the only fully characterized example of this type up to 1995. Methyl triflate methylates the compound at N-1 and gives a phosphonio methylene diazaphosphole cation (30). 

Another cationic 3-phosphonio-l,2,4-diazaphosphole derivative (molecular structure in Table 1) results from the reaction of (Ph3PCPCl)2 with trimethylsilyl azide <96th 422-0 i> (see Section 4.22.8.2). 

The cycloadduct obtained from ethyl diazoacetate and the cyclic phosphaalkene 9-ferf-butyl-1,3-diphenyl- 10-phospha-1,3-etheno- 17/-benzopyran-4(37/)-one underwent spontaneous [3-1-2] cycloreversion and produced ethyl 5-tert-butyl-1,2,4-diazaphosphole-3-carboxylate (163). Still another transformation was found for P-trimethylsilyl-substituted diazaphospholes system 94, which suffered dediazonia-tion under the cycloaddition conditions and yielded phosphaalkene 95 (162) (Scheme 8.22). It was proposed that N2 extrusion and SiMe3 migration occur in concert. On the other hand, the cycloaddition products derived from phosphaalkene 93 and 2,2-dimethyl-1-diazopropane or diazo(trimethylsilyl)methane simply underwent tautomerization to the corresponding A -phosphapyrazoline (162) (94, R = f-Bu H shift R = SiMe3 SiMe3 shift). 

Some highly reactive phosphaalkenes, generated by base-assisted p-elimination at low temperature, have been trapped with appropriate 1,3-dipoles (171). In this manner, dUiydro-l,2,4-diazaphospholes were obtained from phosphaalkenes R R C=PR [R = H, R = Me, R = H (172) R = alkyl, R = C1, R = H (173) R = C02Et, COPh, CONMe2, R = H, SiMes, R = C1 (174)] and ethyl diazoacetate or diazo(trimethylsilyl)methane. By the same strategy, the transient 1-phospha-... 

The 3//-l,2,4-diazaphospholes formed from the reaction of diazomethane and its monosubstituted derivatives (R CH=N2 R = H, alkyl, aryl, acyl, phosphoryl) could not be isolated due to a rapid 1,5-H shift leading to 27/-l,2,4-diazaphospholes 227. When diazo(trimethylsilyl)methane or [bis(diisopropylamino)phosphino]dia-zomethane was used, the l,5-SiMe3 [or PR2, R = N(/-Pr)2] shift completely dominates over the H shift (289,290). In the case of open-chain or cyclic a-diazoketones, cycloadducts 228 cannot be isolated due to rapid acyl shifts giving 229 and ultimately 230 (289). This transformation offers a versatile method to prepare [h]-fused 1,2,4-diazaphospholes from cyclic a-diazoketones and phos-phaalkynes (289). 

Bis[diazo(trimethylsilyl)methyl] phosphines 239 loose only one equivalent of dinitrogen on warming and are transformed into l,2,4(k3)-diazaphospholes 240139 (equation 81). It is obvious to explain this cyclization by intramolecular ketazine formation of a diazocarbene intermediate, but in light of the preceding discussion, speculations about the bond state of this phosphinocarbene (phosphavinyl ylide or phosphaacetylene) are allowed. 

As an example we describe here the synthesis of the l//-l,2,4-diazaphosphole 22 that, on account of its easy accessibility and as parent compound of the class, is of general interest. The synthesis proceeds through condensation of the cation 21. The reaction of 21 with hydrazine involves cleavage of an ammonium salt to furnish the phosphole 23.46 The cation 21 is obtained via a methanaminium chloride—generated as an intermediate from N, A-dimethylformamide and oxalyl chloride—by condensation with tris(trimethylsilyl)phosphine. 

A dihydro-1,2,4-diazaphosphole is obtained by reaction of bis(tri-methylsilyl)amino-trimethylsilylmethylenephosphane with <-Bu-CHN2 resp. trimethylsilyl diazomethane in n-hexane at 0°C (65, 66). Correspondingly, one gets at room temperature the 4,5-dihydro-5,5-diphenyl-3,4-di(2,4,6-trimethyphenyl)-l,2,4-oxazaphosphol with mesityl nitriloxide and the phosphaalkene [Eq. (19)] (64). 

Preparation of Heterocycles. On reaction with methyl esters, diazo(trimethylsilyl)methyllithium (2 equiv) gives 2-substituted 5-trimethylsilyltetrazoles in 50-90% yield (eq 9). Similarly, reaction with nitriles gives 1,2,3-triazoles in high yield (eq lO). Reaction with (Me3Si)2C=PCl leads to 1,2,4-diazaphospholes (eq ll).i ... 

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