SYNTHETIC EQUIVALENTS OF 2-LITHIOPHOSPHININES - NEW ROUTES TO 2-FUNCTIONAL PHOSPHININES

Two routes converting 2-bromophosphinines into 2-functional phosphinines are described. In the first one, a [2 + 4] cycloadduct between the 2-bromophosphinine, 2,3-dimethylbutadiene, and sulfur is first formed. On this adduct, a bromine to lithium exchange is performed by phenyllithium in THF at low temperature. This lithium derivative is converted into a functional derivative by reaction with an electrophile. Then, the 2-functional phosphinine is obtained by a combined reduction-cycloreversion using P(CH2CH2CN)3 as the reducing agent at ca. 180-degrees-C. A 2-(trimethylsilyl)- and a 2-(diphenylphosphino)phosphinine were thus prepared. In the second route, a bromine to lithium exchange is performed on a (2-bromophosphinine)pentacarbonyltungsten complex by phenyllithium in THF at -80-degrees-C. The 2-functional phosphinine is recovered from its complex by heating with Ph2PCH2CH2PPh2 at 110-degrees-C in toluene. A 2-iodo-, 2-(trimethylsilyl)-, and 2-[(diphenylphosphino)pentacarbonyltungsten]phosphinine were thus obtained. An intermediate [2-(ethoxycarbonyl)phosphinine]pentacarbonyltungsten complex readily adds water to give the corresponding 1-hydroxy-1,6-dihydrophosphinine complex.