Stereoselective PCO/POC-Rearrangement of P–C-Cage Phosphorane in the Reaction of 4,5-Dimethyl-2-(2-oxo-1,2-diphenyl)ethoxy-1,3,2-dioxaphospholane with Hexafluoroacetone

Interaction
of 4,5-dimethyl-2-(2-oxo-1,2-diphenyl)­ethoxy-1,3,2-dioxaphospholane,
bearing a carboxyl group in the γ-position with respect to the
phosphorus atom and obtained from d,l-butanediol, with hexafluoroacetone (CCl4, −40
°C) leads to the simultaneous formation of regio- and stereoisomeric
cage-like phosphoranes with phosphorus–carbon and phosphorus–oxygen
bonds with a high stereoselectivity (>95%), whose structure was
determined by 1D and 2D NMR spectroscopy and XRD. When stored as a
solution in dichloromethane for one month, the PCO-isomer rearranges
into the thermodynamically more stable POC-isomer of the cage-like
phosphorane. Mild hydrolysis of the PCO/POC-isomers proceeds with
a high chemoselectivity and leads to the formation of P­(IV)-dioxaphospholane
derivatives. Acidic hydrolysis of the POC-isomer leads to the formation
of an oxirane derivative with an unexpectedly high stereoselectivity
(>95%). DFT calculations (using the PBE functional) allowed us
to obtain structures and energies of the initial phospholane, reaction
products (PCO/POC-isomers), and an intermediate P­(V)-oxaphosphirane.