Diketones from ozonolysis of fused 3‐phospholene oxides: Cyclizations to 3‐phosphorinone and to 1,4‐dihydro‐1,4‐azaphosphinine derivatives

Abstract

Abstract1‐R‐3‐Methyl‐2,4,5,6,7,7a‐hexahydro‐1(H)‐phosphindole 1‐oxide and 1‐R‐3‐methyl‐6‐methoxy‐2,8,9,9a‐tetrahydro‐1(H)‐benzo[e]phosphindole 1‐oxide (R = Me or Ph) were prepared and ozonized at −78°C to give diketones in good yield. The intramolecular aldol condensation was performed on certain of these ketones to give multicyclic 3‐phosphorinone derivatives. In some cases, double‐bond rearrangement into the ring‐fusion position was encountered. The 1‐phenyl derivative in the benzophosphindole series could not be cyclized due to ready displacement of the P fragment from the tetralone system. The diketones reacted with ammonium acetate to give multicyclic derivatives of the 1,4‐dihydro‐1,4‐azaphosphinine ring system. 1,2,3,4,5,6,7,8‐Octahydro‐3‐oxo‐1‐phenylphosphinoline 1‐oxide was used to demonstrate the value of the bicyclic 3‐phosphorinones as precursors of 1‐phosphadecalone derivatives. The carbonyl group was protected as the ethylene ketal and the double bond (as well as the benzene ring) was hydrogenated with ease. Hydrolysis gave the 1‐phospha‐3‐decalone derivative. Reduction of the same 3‐phosphorinone with NaBH4 gave a mixture of diastereomeric alcohols.