Synthesis of B-alkyl derivatives of o-carborane by alkylation under electrophilic conditions; Scope and limitation

Abstract

The reaction of o-carborane with 13 alkylation agents in CS2 over AlCl3 using different ratios of reactants was investigated. Alkylation succeeded with CH3X, C2H5X and i-C3H7X whereas other used agents failed. Only i-C3H7Br alkylated in nitromethane. A rich mixture resulted even with o-carborane: RX 1 : 1 ratio. In the presence of H2SO4 o-carborane was isopropylated with i-C3H7OH, no other alcohols or olefins reacted. Alkyls enter stepwise B-9(12) > B-8(10) > B-4(5,7,11) positions, facilitating always the introduction of further alkyl into the skeleton. On ethylation, the most ethylated product was 4,5,7,8,9,10,12-(C2H5)7-1,2-C2B10H5. Seven B-alkyl and polyalkyl derivatives were isolated as individua. With C6H5Br-AlCl3 no reaction occurred at 27 °C, while only a transfer of Br into 9-position was observed at 127 °C. Possible mechanisms of B-substitution under electrophilic conditions are discussed.