Unusual Closure of the Ten-Vertex Nido Cage via Alkylation: Regiospecific Synthesis of 3-Alkyl Derivatives of closo-1,2-C₂B₈H₁₀

Abstract

Alkylation of the [nido-5,6-RCBH] anions (where R = H and Me) with alkyl halides (RX, where R = primary and secondary alkyls) in boiling tetrahydrofuran (THF) proceeds via unusual H elimination, followed by cage closure to give a series of the neutral closo-1,2-RCBH-3-R derivatives in ∼70-80% yields. In contrast, treatment of the unsubstituted [nido-5,6-CBH] anion with tert-butyl bromide (t-BuBr) led to the formation of the parent closo-1,2-CBH in >85% yield. The constitution of all compounds isolated has been confirmed unambiguously by multinuclear (B, H, andC) nuclear magnetic resonance measurements and α-shift correlation assessments.

Synthesis of closo-1,2-H2C2B8Me8 and 1,2-H2C2B8Me7X (X = I and OTf) Dicarbaboranes and Their Rearrangement Reactions

“…Path A of the next Scheme represents the recently published high-yield conversion of the nido -5,6-R 2 C 2 B 8 H 10 ( 1a ) , carborane into the closo -1,2-H 2 C 2 B 8 H 7 -3-Me ( 2e ) compound. The latter compound 2e was tested as an alternative reagent for further methylation syntheses in the closo -10-vertex dicarbaborane chemistry.…”

“…The latter compound 2e was tested as an alternative reagent for further methylation syntheses in the closo -10-vertex dicarbaborane chemistry. While the methylation of 2e in neat MeI (48 h, reflux) in the presence of a stoichiometric amount of anhydrous AlCl 3 (∼7 equiv) generated the permethylated closo -1,2-H 2 C 2 B 8 Me 8 ( 2c ) in ∼90% yield (path B), the same reaction with 1,2-Me 2 C 2 B 8 H 7 -3-Me ( 2f ) to give 1,2-Me 2 C 2 B 8 Me 8 ( 2d ) did not come to end, again for the same steric reasons as discussed above. Nonetheless, the reaction with the “pre-methylated” substrate 2e represents a good alternative to the synthesis of 2c as that of path A of Scheme .…”