Synthesis of New Substituted Dibenzosuberones

The First Efficient Synthesis and Optical Resolution of Monosubstituted Cyclotribenzylenes

“…Following a known procedure, 3-bromo-dibenzosuberone (17) was prepared in three steps from commercially available starting materials. 19,20 Condensation of p-bromophenyl acetic acid 14 with phthalic anhydride (13) in the presence of sodium acetate at 230-240 °C gave the corresponding phthalide 15 in 82% yield. 20,21 Subsequent reductive ring opening with aq hydroiodic acid/red phosphorus lead to the corresponding benzoic acid derivative 16 in 85% yield, which could be cyclized to the 3-bromo-dibenzosuberone (17) using polyphosphoric acid (64%).…”

“…19,20 Condensation of p-bromophenyl acetic acid 14 with phthalic anhydride (13) in the presence of sodium acetate at 230-240 °C gave the corresponding phthalide 15 in 82% yield. 20,21 Subsequent reductive ring opening with aq hydroiodic acid/red phosphorus lead to the corresponding benzoic acid derivative 16 in 85% yield, which could be cyclized to the 3-bromo-dibenzosuberone (17) using polyphosphoric acid (64%). In analogy to work by Slates and Looker,19c,22 the introduction of the double bond in the bromo derivative 17 was achieved in very good yields (89%) by reaction with phosphorus pentachloride in phosphorus oxychloride.…”

“…23 However, the reductive work-up after ozonolysis of 19 proved to be more difficult than expected. 24,25 Finally, the use of the borane/dimethyl sulfide complex 26 in dichloromethane was successful and yielded the 5-bromo-2,2¢bis(hydroxymethyl)diphenylmethane (20) in 88% isolated yield. Thus, diol 20 can now be prepared for the first time, even in multi-gram quantities, within a few days!…”