LAMBDA(5)-PHOSPHETES, BENZO-LAMBDA(5)-PHOSPHETES, NAPHTHO-LAMBDA(5)-PHOSPHETES - 4-PI-ELECTRON, 8-PI-ELECTRON, AND 12-PI-ELECTRON SYSTEMS

A number of possible strategies for the preparation of lambda(5)-phosp hetes were tested as follows: cyclopropenium 6 was treated with the li thium salt of diphenylphosphine to give phosphinocyclopropene 7, but 7 did not undergo ring expansion upon photolysis or thermolysis. P-chlo ro-C-trimethylsilyl-substituted ylide 8b reacted with two equivalents of dimethyl acetylenedicarboxylate to afford phosphinine 13 via a tran sient lambda 5-phosphete 12. Addition of aluminum trichlo-ride to P-ha logenated ylides 17a-b led to dihydrophosphetium salts 19a-b, which, u pon treatment with pyridine, isomerized into the 1,2-dihydrophosphet-2 -ium salts 20a-b. Hydrolysis of derivatives 20a-b cleanly afforded pho sphoniums 21a-b,which reacted with NaN(SiMe(3))(2) to give rise to the corresponding lambda 5-phosphetes 22a-b. The benzo-lambda(5)-phosphet e 22a underwent ring expansion reactions with dimethyl acetylenedicarb oxylate and acetonitrile, leading to benzo-lambda(5)-phosphinine and b enzo-1,4 lambda(5)-azaphosphinine in good yields. Derivative 22b was c haracterized by X-ray crystal structure analysis. Ab initio SCF calcul ations, IGLO-C-13 chemical shifts and Delta chi For various benzannula ted derivatives and phosphorus heterocycles are presented.