Stereoselective P 5 ‐Deltacyclene Alkylation, an Efficient Route to New Asymmetric P‐C‐Cage Compounds

Tetra‐ tert ‐butyl‐P 5 ‐deltacyclene 5 represents one of only two asymmetric P‐C cage compounds, which are available in highly enantiomerically enriched versions. This paper reports about stereoselective substitution reactions of 5 to develop the chemistry of optically active P‐C cages further. Electrophilic substitution of the only secondary phosphorus atom P1 of the cage with methyl and benzyl groups was achieved with 92 % and >99 % de, but the yields of the reactions are limited due to competing processes. The uncatalyzed hydrophosphination reaction of a monosubstituted allene and two α,β‐unsaturated carbonyl compounds with 5 proved to be the method of choice. cis ‐Butanone‐P 5 ‐deltacyclene 12 is formed in 92 % yield and with >99 % de and cis ‐pentanone‐P 5 ‐deltacyclene 13a is accessible with >99 % de for P1 and 92 % de for the attached carbon atom at the same time. Besides stereoselectivity, the hydrophosphination reaction of 5 performs with a good regioselectivity. The chiral cage 5 controls the stereoselectivity of its reactions for the cage elements as well as for the α position of a substituent.