Phosphazines diazo compounds

Another method for the preparation of the 1,2,4,5-tetrazine system from a diazo compound was reported by Staudinger and Meyer (19HCA619). They reacted diaryldiazomethanes (321) with triethylphosphine and isolated the phosphazines (322). In moist benzene or chloroform these compounds were transformed into 3,3,6,6-tetraaryl-l,2,3,6-tetrahydro-1,2,4,5-tetrazines (323). This result was only obtained when triethylphosphine was used. The intermediate formation of hydrazones seems unlikely, since these compounds are stable and do not dimerize. A reaction which has a certain similarity to the above was reported by Merrill and Shechter (75TL4527). They obtained 3,6-diphenyl-l,4-dihydro-l,2,4,5-tetrazine (80) when the phosphazine (324) was hydrolyzed. 

Aliphatic diazo compounds may also be used as a source for carbenes, which combine subsequently with tertiary phosphines to give phosphonium ylides. The reaction requires the presence of Cu salts, otherwise phosphazines are formed from the diazo compounds and the phosphines. 

The mesomeric diazo compound lOOa/lOOb, derived from diazo group transfer to the appropriate pyrazol-3-one, was irradiated for 10 h in tetrahydrofuran to give the hydrazone chelated adduct 101 as the only product (78H199) (Scheme 29). Mesomeric lOOa/lOOb reacts also with triphenylphosphine to give intermediate ( /Z)-phosphazine 102 which is extremely sensitive to water and hydrolyzes to EjZ)-hydrazone 103. 3-Hydroxy-5,5-dimethyl-cyclohex-2-enone 104 and 3-hydroxy-inden-1-one 106 readily couple with lOOa/lOOb in the presence of sodium acetate to give hydrazono derivatives 105 and 107, respectively. 

---