lithium in tetrahydrofuran N2 atmosphere; addn. of the cyclic thioether to a soln. of trimethylstannyllithium prepared from chlorotrimethylstannane and lithium at -78°C, warming to room temp.;; cooling to 0°C, addn. of methanol, filtration, addn. of pentane,filtration, washing with satd. soln. of NH4Cl, drying on Na2SO4, evapn.of the solvent, fractional distn.;