1,3‐Dehydro‐o‐Carborane: Generation and Reaction with Arenes

Abstract

Like the importance of benzyne, witnessed in modern arene chemistry for decades, 1,2-dehydro-o-carborane (o-carboryne), a three-dimensional relative of benzyne, has been used as a synthon for generating a wide range of cage, carbon-functionalized carboranes over the past 20 years. However, the selective B functionalization of the cage still represents a challenging task. Disclosed herein is the first example of 1,3-dehydro-o-carborane featuring a cage C À B bond having multiple bonding characters, and is successfully generated by treatment of 3-diazonium-o-carborane tetrafluoroborate with non-nucleophilic bases. This presents a new methodology for simultaneous functionalization of both cage carbon and boron vertices.

Functionalization of Carborane via Carboryne Intermediates

“…In view of that the bond dissociation energy of amine α-C-H bond is relatively smaller than that of ether α-C-H bond [14], we wondered whether α-functionalization of amine could be achieved in a similar way.…”

“…In contrast, only the [2 + 2] cycloadduct was obtained in 78 % isolated yield and the formation of the undesired ene product was suppressed for C2-,C3-disubstituted indole III-3ae (Table 3.2, entry 5). Electron-withdrawing (F, Cl, Br, Ph) as well as electron-donating (Me, OMe, iPr) benzenoid substituents were well tolerated in this reaction (Table 3.2, entries [6][7][8][9][10][11][12][13][14]. The molecular structures of III-4aa, III-4ab, III-4ad, III-4ag, and III-4am were further confirmed by single-crystal X-ray analyses (Figs.…”

“…For cyclic amines, the reaction was much dependent on the ring size due probably to steric reasons [16]. For example, 5-membered cyclic amine II-4m was found to undergo α-carboranylation with a *3.7:1 selectivity for cyclic positions [14][15]. Similarly, the reaction of N-ethylmorpholine II-4p furnished only ethyl carboranylated amine (Table 2.2, entry 16), and no ethereal C-H cleavage was observed.…”

“…as "deboronation." Further deprotonation of the resulting nido-C 2 B 9 H 12 − anion with strong base, such as NaH and n BuLi, gives the corresponding dianion nido-C 2 B 9 H 11 2− , an isolobal analog of cyclopentadienyl anion, C 5 H 5 − , which makes it very useful in synthesis of metallacarboranes [12,13] and B(3)-substituted carboranes [14].…”

“…In view of a growing interest in the applications of carborane-containing molecules in medicine [13], materials science [14], and organometallic/coordination chemistry [15], the development of new methods for the synthesis of such molecules has received considerable attention. For instance, carborane derivatives bearing π-substituents (aryl and heteroaryl) have shown promising photophysical properties as light-emitting materials [16].…”