2-Acetyl- diazaphosphole

GuoetaLhavereported Diels-Alder reaction of differently substituted2-acetyl-[l, 2,3] diazaphospholes, 6 with cyclopentadiene and obtained both endo and exo cycloadducts in moderate yields depending on the reaction conditions (Scheme 28). By quenching the room temperature reaction after only 5 min, endo product 89 was obtained exclusively in 65-75% yields, while prolongation of reaction time to 3 days led to the isolation of only exo product 90 in 50-75% yields [19]. 

Scheme 28 Diels-Alder reaction of 2-acetyl-l,2,3-diazaphospholes...

Recently, [2+3] cycloaddition reaction of 2-acetyl-[l,2,3]diazaphosphole (6) with 9-diazofluorenes (96) has been reported [105, 106], From the reaction in cyclohexane at rt, bicyclic phosphirane 97 was obtained as a result of the loss of nitrogen from the initial cycloadduct (Scheme 30). The cycloadduct, 3-spiro substituted 3H-[l,2,4]diazaphospholo-fused [l,2,3]diazaphosphole (98) could be isolated in good yield at room temperature in one case (R=/Bu) its stability was assigned to the presence of bulky fert-butyl group at 7-position. Use of polar solvent like dichloromethane led to the cyclic trimeric compound 99 (Scheme 30). 

Scheme 30 [3+2] Cycloaddition of 2-acetyl-[l,2,3]diazaphosphole with 9-diazofluorene...

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>. 

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