3‐tert‐Butyl‐Substituted Cyclohexa‐1,4‐dienes as Isobutane Equivalents in the B(C₆F₅)₃‐Catalyzed Transfer Hydro‐tert‐Butylation of Alkenes

Abstract

Cyclohexa-1,4-dienes with a tert-butyl group at C3 are shown to function as isobutane equivalents when activated by the strong boron Lewis acid tris(pentafluorophenyl)borane. The hitherto unprecedented transfer hydro-tert-butylation from one unsaturated hydrocarbon to another is achieved with 1,1-diarylalkenes as substrates, thereby presenting itself as a new way of incorporating tertiary alkyl groups into carbon frameworks. Transient carbocation intermediates give rise to competing reaction pathways that could not be fully suppressed.

Alkyl‐Branched Fatty Compounds: Hydro‐Alkylation of Non‐Activated Alkenes With Haloalkanes Mediated by Ethylaluminum Sesquichloride

“…However, the hydro‐alkylation with primary and secondary haloalkanes such as PrBr, BuI, or i PrBr was not possible. Quite recently, Kees and Oestreich reported on the cationic hydro‐ tert ‐butylation of 1,1‐diarylalkenes as substrate …”

Transfer Hydrocyanation of α‐ and α,β‐Substituted Styrenes Catalyzed by Boron Lewis Acids

“…[10] Theg eneral principle behind this strategy is that the boron Lewis acid abstracts ah ydride from the other saturated position to generate aWheland intermediate that eventually releases the electrofuge. [11] With alkenes as p-basic donor molecules, transfer hydrosilylation [12] and hydrogenation, [13] as well as the formal transfer of isobutane, [14] were realized. [15] As illustrated for the transfer hydrogenation, the hydrogen atom labeled in italic is transferred as ah ydride to the more substituted carbon atom, and the hydrogen atom labeled in bold assumes the role of the proton (Scheme 1, middle).…”

Lewis Acid Catalyzed Transfer Hydromethallylation for the Construction of Quaternary Carbon Centers

“…[10,11] Our laboratory has been investigating cyclohexa-1,4diene-based surrogates of difficult-to-handle compounds for metal-free transfer reactions. [12][13][14][15] As part of this program we previously developed cyclohexa-1,4-dienes 5 and 6 as surrogates of isobutane gas and reported their use in the transfer hydro-tert-butylation of alkenes using the strong boron Lewis acid B(C 6 F 5 ) 3 (Scheme 1, top). [14,16] Hydride abstraction from the bisallylic position of the surrogates led to formation of the tert-butyl-substituted Wheland intermediates 7 + and transfer of the electrofugal tert-butyl group to the terminus of 1,1diaryl-substituted alkenes.B orohydride addition to the resulting benzylic tertiary carbenium ion delivered formally anti-Markovnikov alkylation products such as 2.H owever, this process was hampered by side reactions to give 3 and 4, and the substrate scope was quite limited.…”