Retinyl halides

Retinyl halides are very unstable compounds. The tertiary alcohol (594) underwent an allyl rearrangement reaction with phosphorus tribromide or phosphorus trichloride at low temperatures to give the halide (595) (Surmatis and Thommen, 1969). 

As expected, direct synthesis of a retinyl phosphonate from triethyl phosphite and the thermally unstable retinyl halides (595) via a Michaelis-Arbuzov reaction was unsuccessful, so another route had to be employed (Surmatis and Thommen, 1969). The diol (412) was reacted with phosphorus tribromide to give the rearranged dibromide (596), which was converted with triethyl phosphite to the phosphonate. It proved possible to reduce (597) selectively to llZ-retinyl phosphonate (598) over a Lindlar catalyst. 

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