Vinylcyclohexene regioselective

The thermal instability of 37 reduces its applicability with poorly reactive dienes such as vinylcyclohexene and its derivatives 38, unless high pressure (HP) is employed. Ultrasound is not only effective in promoting the cycloaddition of 37 with 38, but sometimes also improves the regioselectivity. Some data are illustrated in Table 4.8 and compared with cycloadditions in refluxing benzene and under high pressure. The reactions of 37 with reactive dienes such as cyclopentadiene and l-(trimethylsiloxy)-1,3-butadiene give a good yield of type D adducts under mild conditions, while with less reactive dienes, such as isoprene and butadiene, poor results are obtained. 

A comparative study of the regioselectivities of monocyclopropanation of limonene and 4-vinylcyclohexene in systems using acetyl chloride promoted diiodomethane with zinc dust and copper(I) chloride in diethyl ether, with diethylzinc in toluene and with triethylaluminum in toluene/dichloromethane showed that the procedure using diethylzinc in toluene exhibited the least steric hindrance toward cyclopropanation at more highly substituted, electron-rich double bonds. ... 

In the presence of a phase-transfer catalyst the cobalt carbonyl-catalysed reaction of dienes with methyl iodide and carbon monoxide (room temp., 1 atm) produces dienones with high regioselectivity. 1-Vinylcyclohexene undergoes acylation only at the least substituted carbon atom of the diene to give the E-isomer (26) in 42% yield. With isoprene acylation occurs at the terminal carbon... 

Catalysts (63) and (64) show significant difference in regioselectivity in the cis-epoxidation of 4-vinylcyclohexene, causing predominant oxidation at the ring alkene position and at the terminal position, respectively. DPT calculations attribute the differences to the geometry and the electronic parameters of the reactants or the charges from the natural population analysis of the substituents of the oxazoline ligands. ... 

---