Synthesis of alkylidenephosphiranes by extrusion of nitrogen from 3-alkylidene-4,5-dihydro-3H-1,2,4-diazaphospholes

Cycloaddition Behavior of 1,2‐Thiaphospholes: Reactions with Diazocumulenes and with Cyclopentadiene

“…[27] and references cited therein) converts intermediates 10 into bicyclic alkylidenephosphiranes 6. The same diazo dipoles 1 or 2 react with acyclic phosphaalkenes [23,27,28] and with 2-acyl-1,2,3-diazaphospholes [16] to give cycloaddition products analogous to 9 that are stable enough to be isolated and are dediazoniated only at elevated temperature. In the diazaphosphole case, the thermal decomposition of the cycloadducts leads to tricyclic compounds related to 4.…”

“…[22] A comparison with the related 2-alkylidenephosphirane [23] 8 can be made, which has a similar 31 P chemical shift (R 1 ϭ tBu: δ P ϭ Ϫ134.5 ppm). The signals of the tetracoordinate ring carbon atom in 6a and 8 differ by only 5 ppm, while that of the olefinic ring carbon atom in 6a is shifted to higher field by 22 ppm (6a: δ C ϭ 92.8 ppm, 1 J P,C ϭ 72.9 Hz; 8: δ C ϭ 114.8 ppm, 1 J P,C ϭ 47.6 Hz).…”

Photochemical Isomerizations of 5-Alkylidene-4,5-dihydro-3H-1,2,4(λ3)-diazaphospholes (4-Phosphapyrazolines): (5→4) Ring Contraction Generates Azomethineimine Dipoles

“…This transformation starts above 150 8C and is rapid at 240 8C. We propose (Scheme 3) that the initial step of the fragmentation reaction is nucleophilic attack by the phosphorus atom at the carbonyl group, followed by elimination of triisopropylsilyl isocyanide (6). The latter compound rapidly equilibrates with Scheme 3. its thermodynamically more stable isomer 7, which was identified by its IR spectrum.…”

“…We have recently found that 4-alkylidene-4,5-dihydro-3H-1,2,4(l 3 )-diazaphospholes 1, easily obtained by [32] cycloaddition of 1-diazo-2-siloxyethenes to phosphaalkenes, [6] are distinctly more thermally stable than similar 4-phosphapyrazolines I lacking the exocyclic double bond. Nevertheless, extrusion of molecular nitrogen from 1 (R 1 tBu, 1-adamantyl, Me, 4-anisyl, 4-nitrophenyl) can be achieved in boiling toluene.…”

“…The 5-alkylidene-4,5-dihydro-3H-1,2,4(l 3 )-diazaphospholes 1 a ± d were prepared as reported. [6] 1-[(tert-Butyldiphenylsilyl)imino]-3,3-dimethyl-1-[diphenylmethyleneamino-(2,4,6-trimethylphenyl)phosphino]-butan-2-one (2 a): A vigorously stirred solution of 1 a (642 mg, 1.20 mmol) in diethyl ether (50 mL) was cooled to 0 8C and irradiated for about 1 h; irradiation of a solution in pentane at À 40 8C was also tested and gave the same results. The solution was allowed to warm to room temperature, and the solvent was removed at 0.002 mbar.…”