4,6-Dimethyl-o-quinone Methide and 4,6-Dimethylbenzoxete

Abstract

4,6-Dimethyl-o-quinone methide (4) was produced by FVP of alcohol 3 or of the trimer 6 and matrix isolated in Ar at 7.6 K. Photolysis of 4 with long wavelength light (>345 nm) at this temperature afforded 4,6-dimethylbenzoxete (5), which was observable up to room temperature in the solid state in the absence of water. 5 can be converted back to 4 by UV irradiation at 254/190 nm. Quantum chemical calculations on the thermal interconversion of 4 and 5 indicate activation barriers of the order of 40 kcal/mol for 4 → 5, and 30 kcal/mol for 5 → 4. The dimer, trimer, and tetramer (8, 6, and 7) of 4 are characterized.

Polymers Based on Phenols

“…Solomon, and Wentrup and coworkers 85 have recently observed and isolated quinone methide 31 at low temperature by flash vacuum pyrolysis 86,87 (FVP) of 27, which was sublimed at ca 45…”

Formation of Cumulenes, Triple-Bonded, and Related Compounds by Flash Vacuum Thermolysis of Five-Membered Heterocycles

“…This is a simple method for the production of dilute solutions of fulvene in benzene. [22c] o-Quinone methide 21 is generated from 20 both photochemically [23] and thermally, [24] and it can exist in photochemical equilibrium with benzoxete 23. The latter can be stabilized by simple methyl substitution in the aromatic ring, but undergo thermal ring opening to 21.…”

“…The latter can be stabilized by simple methyl substitution in the aromatic ring, but undergo thermal ring opening to 21. [24] Scheme 2…”

“…The benzannuleted pyrroledione isatin (24) should then logically be a precursor of the ketenimine 27 (Scheme 3). This, however, is an unstable compound, which tautomerizes to cyanocyclopentadiene (mainly the 1-isomer 28, accompanied by a little of the 2-isomer 29).…”

Kinon-metidi (I. dio): Reaktivni međuprodukti u kemiji fenola i njihova primjena u organskoj sintezi

“…Metode sintetske (termičke) priprave QM-a iz različi-tih prekursora prikazane su shemom 8. One uključuju oksidaciju fenola, 40 pirolizu dimera kinon-metida, 41 eliminaciju nitrila iz 1,2-benzoksazina, 42 eliminacije vode, 40 alkohola, tiola, karbonilnih spojeva, amina i desililaciju induciranu * U ovom pregledu upotrebljavat će se izraz "generiranje QM", koji je uobičajen u publikacijama na engleskom jeziku (generation of quinone methides). Izrazi dobivanje/priprava/sinteza QM-a žele se izbjeći s obzirom na to da mogu pogrešno navoditi na zaključak da se radi o spojevima koji su stabilni i izolabilni, što je rijetkost.…”