Regioselective Nucleophilic Alkylation/Arylation of B–H Bonds in o-Carboranes: An Alternative Method for Selective Cage Boron Functionalization

Abstract

A new protocol for regioselective nucleophilic cage B−H substitution in o-carboranes has been proposed that is complementary to the strategies of transition metal catalysis and electrophilic substitution. Magnesium-mediated site-selective nucleophilic cage B-(3,6)−H and B(9)−H substitution reactions of ocarboranes give a series of B(3,6)-dialkylated and B(9)alkylated/arylated o-carboranes in high yields. Both steric and electronic factors of cage C substituents play crucial roles in controlling the site selectivity.

Highly selective palladium-catalyzed one-pot, five-fold B–H/C–H cross coupling of monocarboranes with alkenes

“…Likewise, when it comes to the preparation of inorganic–organic hybrid molecules, the construction of E–C bonds (E = main group element other than C) is equally important. For icosahedral carboranes, the modification of boron vertices traditionally relies on direct electrophilic substitution or electrophilic halogenation followed by transformation to a B–X (X = C, N, O, S, P) bond 9,10. Drawbacks of these approaches are harsh conditions, limited control over selectivity of the substituted positions and moderate overall yields.…”

Rh‐Catalyzed Decarbonylative Cross‐Coupling between o‐Carboranes and Twisted Amides: A Regioselective, Additive‐Free, and Concise Late‐Stage Carboranylation

“…To our best knowledge, cross‐coupling which is accompanied with rearrangement of the twisted amide's scaffold has not been observed before. Besides, this coupling is also different from recently reported coupling between t Bu and B(4) via a nucleophilic substitution [19b] . We considered that the large steric hindrance of o ‐carboranyl and third order C(sp 3 ) center is the primary cause for the unique rearrangement.…”

One-Pot Synthesis of B-Aryl Carboranes with Sensitive Functional Groups Using Sequential Cobalt- and Palladium-Catalyzed Reactions

“…A series of aryl derivatives of ortho-carborane were prepared by Pd-catalyzed B-H activation reactions with aryl iodides under functional group assistance or by intramolecular cyclization via Pd-catalyzed B-H activation involving pendant ortho-bromoaryl groups [43]; however, these reactions are currently of academic interest rather than real synthetic methods. Of greater interest is the direct arylation of 1,2-bis(dimethylphenylsilyl)-ortho-carborane 1,2-(PhMe 2 Si) 2 -1,2-C 2 B 10 H 10 with arylmagnesium chlorides in diethyl ether, followed by the removal of the silyl protective groups with K 2 CO 3 in acetone [44]; however, this approach gives only moderate yields of 9-aryl-ortho-carboranes and is not tolerant to many functional groups.…”