Dihydro-1,2,4-diazaphosphole

In certain cases, 4,5-dihydro-1,2,3-diazaphospholes rather than 3,5-dihydro-1,2,4-diazaphospholes are formed from the [3-1-2] cycloaddition reaction of diazo compounds with phosphaalkenes. This regiochemistry was encountered in the reaction of (mesityl)P=CPh2 with diazodiphenylmethane and was attributed to steric factors (164). Electronic factors may explain the orientation found in the... 

The P=C bond of ), a -phosphoranes is also accessible to a 1,3-dipolar cycloaddition reaction. The formation of 97 (Scheme 8.23), of 3,5-dihydro-1,2,4-diazaphosphole sulfide 132 from an amino(methylene)thioxophosphorane (190) and of phosphirane imine 133 from an amino(imino)alkylidenephosphorane (191) (Scheme 8.29) illustrate the chemical behavior of phosphaalkenes containing a A, a -phosphoms atom. 

Some highly reactive phosphaalkenes, generated by base-assisted (3-elimination at low temperature, have been trapped with appropriate 1,3-dipoles (171). In this manner, dihydro-1,2,4-diazaphospholes were obtained from phosphaalkenes R R2C=PR3 [R = H, R2 = Me, R3 = H (172) R1 = alkyl, R2 = C1, R3 = H (173) R1 = C02Et, COPh, CONMe2, R2 = H, SiMe3, R3 = C1 (174)] and ethyl diazoacetate or diazo(trimethylsilyl)methane. By the same strategy, the transient 1-phospha-... 

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). 

Keywords 1,3,2-diazaphospholes 1,3,2-diazaphospholenes 1,3,2-diazaphosphinines 2,3-dihydro-l,3,2-diazaphosplinines diketiminto-phosphenium ions N-heterocyclic phosphines N-heterocyclc phosphenium ions 1,2,3-diazaphospholenium ions... 

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],... 

Lithiumalkyls (R = Me, Bu, Bu ) as well as lithium diisopropylamide (R = NPr)) add readily to the P=C bond of 2,5-dimethyl-l,2,3-diazaphosphole (66) <84PS(21)97,87JOM(319)49). With methyl iodide and organotin chlorides the adduct (67) yields 4-substituted dihydro-1,2,3-diazaphospholes (68). Only in the case of reaction of methyllithium (R = Me) is lithiation at C-4 observed as a minor side reaction (Scheme 23). 

Treatment of a 2-acetyl-3-methoxy-3,4-dihydro-l, 2,3-diazaphosphole with phenylhydrazine gives the 2-phenyl derivative in addition to the deacylated 1,2,3-diazaphosphole <77ZOB576>. 

Hydrochlorides of 2//-l,2,3-diazaphospholes (Section 4.22.5.1.2) i.e. 3-chloro-3,4-dihydro-2/7-1,2,3-diazaphospholes generated in situ from a ketone hydrazone and PCI3 (see Section 4.22.5.2) are... 

Phosphaalkenes that possess a A, a -phosphorus atom can be isolated when appropriately substituted (151). These systems exhibit a much more expressed dipolarophilic than dienophihc reactivity, probably as a consequence of the polarity of the P=C bond. The [3 + 2] cycloaddition of diazo compounds with phosphaalkenes 87 leads to 4,5-dihydro-3//-l,2,4-diazaphospholes 88 (Scheme 8.21) that are not always isolated. Quite often, ehmination of molecular nitrogen occurs during the cycloaddition at or below 20 °C. In other cases, N2 extrusion is achieved at... 

The potential usefulness of 3//-l,2,4-diazaphospholes for the synthesis of other phosphorus heterocycles was demonstrated using 234 (Scheme 8.55) which, after UV irradiation at —40°C, gave a 5 1 mixture of 4,5-dihydro-3//-phospholes 235 and 236. The latter compound is the hrst example of the previously unknown 2H-phosphirene system (288). This reaction probably proceeds via a photochemical ring opening of 234 and formation of a phosphavinyl carbene. 

A synthesis of 4-cyano-2,3-dihydro-3-hydroxy-2,5-diphenyl-l//-l,2,3-diazaphosphole 3-oxide from hydrazidoyl halide PhC(Cl)=NNHPh and diethylphosphonoacetonitrile in the presence of sodium ethoxide was reported <2004PS(179)521 >. 

Entsprechend liefert 2,5-Dihydro-1,2,3-Diazaphosphol mit Diphenylnitrilimin a,j3-Bis-[hydrazono]-phosphonoxide16 ,a. 

Bestimmte 3,4-Dihydro-2H-l,2,3-diazaphosphole reagieren mit 2-Azido-phenol unter Erhalt dcr Konfiguration (cuts, trans) zu spirocyclischen Phosphoranen36 ... 

The 4,5-dihydro-37/-l,2,3-diazaphosphole 34 produced by a [3+2] cycloaddition reaction of diphenyldiazomethane with a phosphaalkene is unstable and decomposes by extrusion of Na and formation of a new P-C bond yielding the phosphirane 35 (Scheme 14) <2001ZFA1241>. 

The availability of phosphaalkenes led to a second route to phosphiranes with diazoalkanes as cycloaddition partners compare with Scheme 14. The first formed 4,5-dihydro-3//-l,2,4-diazaphospholes 43 decompose under the influence of light and extrusion of nitrogen to form the bis(methylene) phosphoranes 44, which cyclize in a 47t-electro-cyclic closure to the phosphiranes 45 (Scheme 17) <1996CHEC-II(I)298>. For the theoretical background, see Section 1.08.2.1.1, and for analogous reactions see <1995CC25> and <1997CB779>. 

The formation of dialkyl phosphoramidates from trialkyl phosphites and benzothiazol-2 1 sulphenamides has been discussed. (Diaryloxyphosphlnyl)phosphoramidic acids have been prepared by a short conventional sequence.A convenient one-pot synthesis of 1,3-dihydro-l,3,2-diazaphosphole 2-oxides (90)... 

The only known example of this ring system is the 3,4-dihydro-22 -compound (193) which was reported to be formed by the action of tris(dimethylamino)phosphine on monobenzylidene diaminomaleonitrile. On standing in acetonitrile it undergoes an unusual ring contraction ben-zylidene bisdimethylaminoaminal and a proton are eliminated and the anion of dicyano-1,3,2-diazaphosphole is formed (Scheme 39) <84CC183>. 

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>. 

The other approach to P-ylides based on the nucleophilic addition of phosphorus(HI) reagents to the terminal carbon atom of 1,2-diaza-1,3-butadienes has continued to find application. The reaction with dialkyl-phosphonites or phosphorus(III) amides under solvent-free conditions (and in the presence of atmospheric moisture) was found to be a convenient approach to a-phosphanylidene hydrazones (42). The linear ylides (42) in THF solution undergo further intramolecular transformations to give 1,2,3X -diazaphospholes (43) in the case of phenylphosphinite as a starting substrate or 5-oxo-4-phosphoranyidene-4,5-dihydro-l/f-pyrazoles (44) using tris(dialkylamino)phosphine. 

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