VINYLPHOSPHONIUM SALTS AND ALLENES FROM CARBONYL-COMPOUNDS USING TITANIUM-SUBSTITUTED YLIDES

(E)-Vinylphosphonium salts are conveniently obtained from the reaction of carbonyl compounds with titanium-substituted ylide species (Me2N)( 3)P=CHTi(OiPr)Cl-2 or (Me2N)(3)P=CHTi(OiPr)(2)Cl. While a wide variety of nonenolizable aldehydes are tolerated, the steric bulk surrounding the ylide carbon limits the process to highly activated or unhindered ketones. The vinylphosphonium salts may be converted to allenes by de protonation and condensation with a second aldehyde, thus accomplishin g a two-step double olefination allene synthesis. This methodology, al ong with a previously reported one-pot reaction, comprises the most co nvenient route available for the synthesis of 1,3-disubstituted allene s. The metal-substituted ylide reagent may be generated in situ from c ommercially-available starting materials. Two representative vinylphos phonium salts were shown to undergo reversible isomerizatian to the (Z )-form upon irradiation.