Thermal Pericyclic Tandem Reactions

Abstract

Gas phase thermal isomerizations of twelve acetylenic systems, all of which can in principle undergo two successive pericyclic steps, are described. The substrates, the syntheses and spectroscopic properties of which are presented, are formal derivatives of but-2-yne, with different functional groups in the 1-and the 4-positions. The Cope, Claisen, Claisen ester, retro-ene, 1,5-hydrogen shift, and 1,5-homo

Model Reactions for the Synthesis of Azacorannulenes and Related Heteroaromatic Compounds

“…Flash vacuum pyrolyses were performed in our standard apparatus, [1] involving a tubular furnace containing an empty quartz tube (l ϭ 60 cm, o.d. ϭ 4 cm), which was connected at one end to a vaporization flask (heated externally by a kugelrohr oven) and at the other, via a cold-trap (liquid nitrogen), to a high vacuum line.…”

“…After solvent removal, the remaining oil was purified by flash chromatography (silica gel, diethyl ether) to afford 21 (0.5 g, 43% with respect to 18) as a yellow oil. 1 …”

“…The oil obtained after solvent removal was purified by flash chromatography (silica gel; diethyl ether) to afford 11 (0.98 g, 48%) as a reddish oil. 1 (24) was prepared from 23 by a published procedure. [25] A mixture of 24 (10.29 g, 28.0 mmol), 1-chloro-2-iodobenzene (20, 8.2 mL, 16.0 g, 67.1 mmol), and Pd(PPh 3 ) 2 Cl 2 (0.41 g, 0.6 mmol) was heated at 100°C under nitrogen for 5 d. After the mixture had cooled to room temp., dichloromethane was added, and the mixture was treated with 3  hydrochloric acid.…”

“…1 (10 mL). After the mixture had been stirred for 1 d at room temp., the solvents were removed in vacuo and the remaining oil was dissolved in dichloromethane.…”

“…200°C (decomp.). 1 5 mL), and a small amount of CuI were added to a solution of 2-chloro-3-iodopyridine [39, 0.44 g, 1.8 mmol, prepared from 2-chloropyridine (38) according to ref. [27] ] in triethylamine (20 mL), and the mixture was stirred for 5 h at room temp.…”