Xanthen-9-ylidene protecting groups in glycerol chemistry

The preparation of racemic, (S)- and (R)-1,2-O-(xanthen-9-ylidene)glycerol 17a, 20a and 23a and racemic, (S)- and (R)-1,2-O-(2,7-dimethylxanthen-9-yli dene)glycerol 17b, 20b and 23b is reported. The racemic derivatives 17a and 17b are converted into their stearate esters, which are then treated with dichloroacetic acid and pyrrole under mild conditions to give racemic 1-O-s tearoylglycerol 25 in good yield. The xanthen-9-ylidene and 2,7-dimethylxan then-9-ylidene residues are incorporated into 9,9-di(pyrrol-2-yl)xanthene 3 6 and 2,7-dimethyl-9,9-di(pyrrol-2-yl)xanthene 37. These by-products are ea sily removed by treatment with iron(III) chloride in diethyl ether solution . What are believed to be enantiomerically pure (R)- and (S)-1-O-stearoylgl ycerol 28 and 5 are similarly prepared in good yields from (S)- and (R)-1,2 -O-(xanthen-9-ylidene)glycerol 20a and 23a.