Synthesis of Di-substituted Proazaphosphatrane and Its Application in Carbon-carbon Double-bond Isomerization

Diisopropyltren was synthesized from the reaction of tren with benzaldehyde in toluene, followed by reducing the imine intermediate with NaBH4, and debenzylation catalyzed by 10% Pd/C in methanol. It was then converted to its corresponding azaphosphatrane via ring-closing reaction of HMPT and triflic acid. Deprotonation of azaphosphatrane with potassium t-butoxide afforded the target diisopropyl proazaphosphatrane 1d. A comparative study of compound 1d for isomerization of allylic system and methylene-interrupted diene system revealed that compound 1d is more efficient than its tri-substituted analoque(1b). In acetonitrile at 40 °C, allylaromatics were selectively isomerized to 1-arylpropene generally in an isolated yield more than 95% with trans, cis molar ratios in a range of 87/13 to 96/4. Allyl phenylsulfide was converted to 1-phenylthiopropene(molar ratio of Z/E=54/46) in a yield of 93%―95%. Methylene-interrupted dienes were also isomerized in high yield.