Gas-Phase Intramolecular Diels-Alder Reactions of 2,3-Dimethylene-2,3-Dihydrofurans; Formation of 9-Methylanthracene and Anthracene by Pyrolysis; and Preparation of Cyclopentadienones by Flash Vacuum Pyrolysis

摘要

The intramolecular Diels-Alder reactions of 2,3-dimethylene-2,3-dihydrofurans have been investigated through the pyrolysis of 2-alkenyl-3-furylmethyl benzoates. Under FVP conditions each of the 2,3-dimethylene-2,3-hydrofurans can undergo an intramolecular Diels-Alder reaction or 1,5-hydrogen shift to give the corresponding tricyclics 4c,t, 5c,t, and 6c,t and 1,5-hydrogen shift products 36c,t and 37c,t. FVP of 1,5-dibenzocyclooctadienes containing heteroatoms and dibenzosuberanes gave the corresponding tricyclic compounds (benzodifuran, acridine, and anthracene) except 6H,11H-dibenzo(b,f) (1,4)-dioxocin. FVP of the latter gave (2-hydroxybenzyl)-o-benzaldehyde as a major product. A mechanistic study of the regiospecific formation of 9-methylanthracene from the sealed tube pyrolysis the (4 + 4) dimer of o-xylylene is presented. A new method of preparing cyclopentadienones by the pyrolysis of cyclic diethers is presented. Cyclopentadienones including inden-2-one have been utilized in the synthesis of polycyclic compounds. (ERA citation 12:037398)