Pinacol Condensation of Homocubanone. Synthesis and Chemistry of Homocubylidenehomocubane. (Reannouncement with New Availability Information).

摘要

Reductive coupling of homocubanone (1) with TiC14-Zn afforded the corresponding pinacol (3, 21%) and homocubanol (4, 40%). Reaction of 3 with HC(OEt)3 in the presence of benzoic acid afforded cyclic orthoformate 5 (95%), which when heated with benzoic acid at 200 deg C gave homocubylidenehomocubane (2, 95%). When treated with AgNO3-imPregnated silica gel at 25 deg C for 6 days, 2 gradually underwent homocubane-norsnoutane rearrangement, thereby affording 7. Acid-promoted pinacol rearrangement of 3 gave the corresponding pinacolone 6 (61 %). Electrophilic addition of trifluoroacetic acid and of bromine to the C=C double bond in 2 proceeded in both cases via simple 1,2-addition (i.e., without accompanying Wagner-Meerwein rearrangement), thereby affording 8 (64%) and 9 (24%), respectively. The structures of 2, 6, 7, and 9 were elucidated via X-ray crystallographic methods. The results of MM2 calculations suggest that there is insufficient driving force provided by relief of steric strain to promote Wagner-Meerwein rearrangement of the carbocation that is produced upon protonation of the C=C double bond in 2. Electrophilic Addition to C=C, Pinacol Condensation, Pinacol Rearrangement, Homocubanone, Strain Energy Calculations (MK2), Homocubvlidenehomocubane.