Stereoselectivity in the Ene reaction of syn- and anti-1-(4-tert-butylcyclohexylidene)-4-tert-butylcyclohexane with singlet oxygen, nitrosyl hydride, nitrosoformaldehyde, 4-phenyl-1,2,4-triazol-3,5-dione, diethyl azodicarboxylate and methyl propiolate

Abstract

The stereochemistries of the ene reactions of syn- and anti-1-(4-tert-butylcyclohexylidene)-4-tert-butylcyclohexane (I and II) with a series of enophiles XY (singlet oxygen, nitrosyl hydride, nitroso-formaldehyde, 4-phenyl-1,2,4-triazol-3,5-dione, diethyl azodicarboxylate and methyl propiolate) to give, by axial or equatorial attack as shown, the allylic adducts III and IV, have been investigated. [graphic omitted]

None of the reactions is stereospecific, the products being as follows (ene, enophile. III:IV): I, ¹O₂, 60–68:40–32; II¹O₂, 33–50:67–50; I, HNO, 10:90; II HNO, 11:89; I, HCONO, 25:75; II, HCONO, 50:50; I, [graphic omitted]O, 17:83; II, [graphic omitted]O, 20:80; I, EtOCONNCO₂Et, 77:23; II, EtOCONNCO₂Et, 27:73; I, HCCCO₂Me, 53:47; II, HCCCO₂Me, 67:33.

The allylic hydroperoxides which are formed by the reaction of singlet oxygen react further with triplet oxygen to give allylic dihydroperoxides. The ene reactions of methyl propiolate are accompanied by the formation of cyclobutenes via cycloaddition.

The stereoselectivities of the ene reactions preclude a concerted suprafacial attack of the eno-philes, but they support the model of the formation of an intermediate CC/XY adduct which can undergo conformational change before the allylic hydrogen atom is transferred.