Leonardus W. Jenneskens

Scope and limitations of the flash vacuum thermolysis approach to small [n]paracyclophanes

Abstract Flash vacuum thermolysis (FVT) of 3-methylene-6-spirocyclohexa-1,4-dienes (2) was investigated as a synthetic approach to small [n]paracyclophanes 1 (1a, n = 8; 1b, n = 7; 1c, n = 6). The method was found to be preparatively attractive for 1a (80% yield), less so for 1b (7% useful yield), and not at all for 1c which was too unstable to survive the conditions of its formation. Besides 1, p-alkylstyrenes (3) and 2-methylbenzocycloalkenes (4) were obtained; the total recovery of monomeric products was good (60–85%). The temperature dependence of the product formation furnished useful information on the mechanisms of formation and decomposition of 1 under the conditions of FVT.

9-Hydroxy [7]metacyclophane

Abstract A new pyrolytic access to a metacyclophane has been found by the flash vacuum thermolysis of spiro[5,7]trideca-l,4-dien-3-one ( 4 ) which gave 9-hydroxy[7]metacyclophane (7) , and 4-(6-heptenyl)phenol (8) . The mechanism of formation of 7 and 8 from the intermediate diradical ( 6 ) is discussed.

Flash vacuum thermolysis of spirocyclohexadienones

Abstract In an attempt to prepare short-bridged hydroxymetacyclophanes 1b-d , the spirocyclohexadienones 2b-d were pyrolyzed by flash vacuum thermolysis (FVT). Instead of 1b-d , variable amounts of 4-(5-hexenyl)phenol ( 4b ), β-hydroxybenzocycloalkenes ( 5b-d ) and 4-(trans-1-alkenyl) phenols ( 6c-d ) were obtained. The formation of these products is explained by invoking cleavage of a spiro bond in 2 under formation of the intermediate diradical 3 which, depending on the length of the aliphatic chain and on the temperature, has several pathways open for isomerization to spin-paired products.