I. the cycloaddition reactions of methyl and (-)-menthyl acrylates with cyclopentadiene on ℓ-alumina; II. the hydroboration of alkenylcarboranes

The hydroboration of representative alkenyl-ortho-carboranes with borane-tetrahydrofuran (BH₃•THF), 9-borabicyclo[3.3.1]nonane (9-BBN), and dicyclohexylborane (Chx₂BH) was investigated systematically to establish the rates, stoichiometry and directive effects in the hydroboration. The cage exerts a profound effect in the rate and the regioselectivity particularly for the vinyl derivatives of carborane. The directive effect observed for vinylcarborane and propenylcarborane with borane results in an considerable amount of α-organoboranes, as compared to β. The directive effect observed for isopropenylcarborane with borane results in the exclusive formation of the β-organoborane. Likewise the directive effect observed for allylcarborane and hexylallylcarborane is significant and favors the internal carbon. With increasing distance from the cage the ability of the cage to direct boron in the internal carbon decreases. Hydroboration with 9-BBN and Chx₂BH results in a remarkable regioselectivity for the terminal position in all cases. The Diels-Alder reaction of cyclopentadiene (CP) with methyl (MA) and (- )-menthyl (MNA) acrylates on alumina of varying catalytic activity has been studied. The diastereophase-selectivity of the reaction of CP with MNA, and particularly the diasteroselectivity of the reaction of CP with MA, are markedly dependent on the activity of the alumina. The results can be explained by two factors: (1) the nature and the number of the active sites on the surface, and (2) the facile retroversion of the cycloadduts on the more activated alumina. The reaction of CP with MA has been used to measure the polarity of the surface being express by the Ω value. The Ω value of the surface of unactivated alumina was shown to be 0.740 ± 0.024 which suggests that the surface has a polarity comparable to ethanol and acetic acid.