Synthesis of 1-phosphaadamantane

The annelation reaction between 1,2,3,6-tetrahydro-1-phenyl-4-(1-pyrrolidinyl)phosphorin 1-oxide (4) and ethyl 2-bromomethyl-3-bromopropanoate (5) yielded a mixture of two stereoisomers of the 3-phosphabicyclo3.3.1]nonane derivative 6. The keto function of 6 was reductively removed to furnish 8 which with LiAlH₄ was reduced to 9. Treatment of 9 with trichlorosilane gave the 1-phenylphosphoniaadamantane 11. The phenyl group of 11 was cleaved with sodium to give the title compound 1, or with NaOH to give the oxide 12 of 1. With benzyl bromide, 1 was quaternized to 13.