in benzene from a suspn. of dihydroxybutenedioic acid and triethylboroxine in benzene the half amt. of benzene was removed by azeotropic distn.; the remaining suspn. was cooled; filtered and the crystn. compd. washed with hexane; further purifn. by high vac. sublimation at ca 130-150°C or crystn. from a large vol. of toluene; elem. anal.;

in benzene to a refluxing suspn. of octahydroxycyclobutane in C6H6 during 20 min dropwise was added diethyl(pivaloyloxy)borane; gas evolution for 1 h; cooled, filtered, washed with pentane; further purifn. by high vac. sublimation at ca 130-150°C or by crystn. from a large vol. of toluene;

C4(BO2Ph)4 and (C2H5)2BOOCC(CH3)3 were stirred and heated at 80°C for 6 h; after cooling pentane was added,; filtered, the colorless solid was thoroughly washed with little portions of pentane. It was sublimed in vac. at 150-170°C; further purifn. by sublimation or by crystn. from a large vol. of toluene; elem. anal.;

a suspn. of dihydroxybutenedioic acid and diethyl(pivaloyloxy)borane was slowly heated to ca 70°C; on completion of gas evolution the mixt. was cooled, hexane was added; crystn. compd. filtered and washed with hexane; further purifn. by highvac. sublimation at ca 130-150°C or by crystn. from a large vol.of toluene; elem. anal.;

in benzene refluxing dihydroxyfumaric acid with (18)O-triethylboroxine in benzene; removing volatiles (reduced pressure), washing (pentane);

in benzene refluxing the boron heterocycle with (18)O-triethylboroxine in benzene (7 h); removing volatiles (high vac.);