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-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.

Facial Synthesis ofo‐Carborane‐Substituted Alkenes and Allenes by a Regioselective Ene Reaction of 1,3‐Dehydro‐o‐carborane

“…[13] The highly polarized CÀBm ultiple bond can also rationalizet hat the selectivity of the CÀHb onds in the ene reactions follows the order:p rimary CÀH > ,s econ- www.chemeurj.org dary CÀH > ,a nd tertiaryC ÀH, which is well in agreement with the acidity of theseC ÀHp rotons. [17] In support of this observation, substrate 6m processing aC F 3 substituent was subjected to this reaction.…”

“…In this regard, our recently reported1 ,3-dehydro-o-carborane (2), [13] featuring ap olarized cage C-B multiple bond, would be an excellent candidate for ene reactions with alkenes and alkynes. Herein, we report ag eneral,h igh-yielding, and regioselective ene reaction of 1,3-dehydro-o-carborane for the straightforward access to cage B(3)-substituted carboranyl alkenes and allenes (Scheme 1).…”

Recent advances in the chemistry of carborynes

“…1) is the most widely M a n u s c r i p t 2 investigated one, probably due to its commercial availability. One important feature of o-carboranes is that they can undergo dehydrogenation to form 1,2-dehydro-o-carboranes (o-carborynes) [3] or 1,3-dehydro-o-carborane [4], two very reactive intermediates featuring a cage C−C or C−B multiple bond, respectively. These two intermediates can be regarded as three-dimensional relatives of 1,2-dehydrobenzene (benzyne).…”

“…During our exploration, we found that o-carboryne exists in two resonance forms, a bonding form vs a biradical form [3d], whereas 1,3-dehydro-o-carborane is best described as a resonance hybrid of a bonding form and a zwitterionic form ( Fig. 1) [4]. o-Carboryne was first reported by Jones in 1990 [3a] and many reactivity studies have been published since then [3d].…”

“…o-Carboryne was first reported by Jones in 1990 [3a] and many reactivity studies have been published since then [3d]. In sharp contrast, 1,3-dehydro-o-carborane has remained elusive until 2014 that our group developed a successful method to generate such reactive intermediate [4]. The cage C−C bond length of o-carboryne is calculated to be 1.365 Å, which is significantly shorter than that of 1.625 Å observed in its parent o-carborane, indicating the presence of multiple bonding character.…”