Methoxymethyl-triphenylphosphonium chloride → 8-Bromo-5-methoxymethylene-2,3,4,5-tetrahydrobenzo[b]thiepine

Participants

Reaction Conditions

Reaction Steps

16.68 g (1.6 eq.) of (methoxymethyl)triphenylphosphonium chloride was suspended in 75 ml of abs. THF and deprotonated between −15° C. and −5° C. by adding via syringe 29.5 ml of 1.6 M n-butyllithium (hexane, 1.55 eq.). The resultant red ylide solution was cooled to −75° C. and treated with 7.82 g (30.4 mmol) of 8-bromo-3,4-dihydro-2H-benzo[b]thiepin-5-one, dissolved in 15 ml of abs. THF. The mixture was then kept for 0.3 h at −78° C. and for 1.25 h at room temperature. Pouring onto crushed ice, twofold extraction with diethylether, washing the organic phase with water, drying over magnesium sulfate, filtration and evaporation of the solvents yielded a crude product which was purified by flash chromatography (SiO2, hexane/ethylacetate 95/5); thereby, 7.39 g of 8-bromo-5-methoxymethylene-2,3,4,5-tetrahydrobenzo[b]thiepine was obtained as E/Z-mixture which was hydrolyzed as follows:

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