Boradigermaallyl: (4+3) Cycloaddition‐Initiated Boron Insertion into Benzene

Abstract

The 2π electron 1,3‐dipole boradigermaallyl, valence‐isoelectronic to an allyl cation, is synthesized from a bis(germylene). It reacts with benzene at room temperature by insertion of a boron atom into the benzene ring. Computational investigation of the mechanism shows the boradigermaallyl reacting with a benzene molecule in a concerted (4+3) or [π4s+π2s] cycloaddition reaction. Thus, the boradigermaallyl acts as a highly reactive dienophile in this cycloaddition reaction with nonactivated benzene as diene unit. This type of reactivity provides a novel platform for ligand assisted borylene insertion chemistry.

Dearomatization of C6 Aromatic Hydrocarbons by Main Group Complexes

“…The reaction proceeds by the insertion of boron into the C−C bond of the cyclohexanediene 37 , which is initially generated by [4+3] cycloaddition of 36 with benzene (Scheme 4c). In the same report, the authors also presented the [4+3] cycloaddition of 36 with anthracene [31] …”

“…In the same report, the authors also presented the [4 + 3] cycloaddition of 36 with anthracene. [31] In 2003, the first example of a [2 + 4] cycloaddition of arenes by a low-valent aluminum compound was reported by Power and co-workers (Scheme 5a). [32] The reduction of 1,2-diiododialane Ar 2 Al 2 I 2 39 a [Ar = 2,6-Dipp 2 C 6 H 3 , Dipp = 2,6-i Pr 2 C 6 H 3 ] with KC 8 led to the generation of the corresponding dialumene 42 a in situ, which can react with toluene to furnish the [2 + 4] cycloaddition product 43 a.…”

Reversible Boron‐Insertion into Aromatic C−C Bonds

“…A boranorcaradiene intermediate was generated by photo‐promoted di‐π‐borate rearrangement and underwent an electrocyclic reaction to afford the benzoborepin structure. Recently, Bettinger and Wesemann reported germylene ligand‐assisted borylene insertion into a C−C bond of benzene promoted by boradigermaallyl [11d] …”

Intramolecular dearomative 1,4-addition of silyl and germyl radicals to a phenyl moiety

“…9 c Reports from Harder, 11 Jones, 12 or Andrada 13 showcase this reaction mode for magnesium and aluminum compounds under reductive or photolytic conditions, clearly indicating the corresponding radicals to be the crucial intermediates (Scheme 2b). The Birch-type addition of silicon and germanium compounds to benzene scaffolds was by now achieved by cycloaddition strategies like the [4 + 3] cycloaddition reported by Wesemann 14 or the [2 + 2] cycloaddition reported by Cummins. 15 In our understanding, the dearomative 1,4-addition to phenyl rings is hard to accomplish with germyl radicals due to their low reactivity compared to group 2 or 13 and the relatively low Ge–C bond energies.…”