Reaktionen frustrierter Lewis‐Paare mit konjugierten Inonen – selektive Hydrierung der Kohlenstoff‐Kohlenstoff‐Dreifachbindung

Abstract

Ungeachtet ihres Namens können frustrierte Lewis‐Paare selektive 1,4‐Additionen an konjugierte Inone eingehen (siehe Schema). Nach Wasserstoffaktivierung durch frustrierte Lewis‐Paare gelingt die selektive Hydrierung der Kohlenstoff‐Kohlenstoff‐Dreifachbindung des Inons in einem Fall sogar katalytisch.

Metal‐Free Hydrogenation of Electron‐Poor Allenes and Alkenes

“…[12,13] Surprisingly, despite all of these achievements, the FLP-promoted catalytic hydrogenation of electron-poor unsaturated systems is still underdeveloped. [14] Herein, in an attempt to address this clear limitation, we describe our efforts towards the catalytic reduction of allenes. These studies indicate that electron-deficient allenes are the most adequate substrates for hydrogenation, probably following a Michael-type hydride addition to the allene.…”

“…To the best of our knowledge, this is the first systematic study on the reduction of electron-deficient unsaturated species employing FLPs. [14] Finally, some considerations about the plausible reaction mechanism will be mentioned. It has been proposed that the FLP-promoted reduction of imines and electron-rich alkenes is initiated by protonation of the substrate, followed by hydride transfer.…”

Unusual Pathway Taken in the Reaction of Bis(alkynyl)diisopropylaminoboranes with B(C6F5)3

“…We had previously shown that some alkynylboranes that were obtained from alkyne/RBA C H T U N G T R E N N U N G (C 6 F 5 ) 2 1,1-carboborations readily underwent E-/Z-isomerization. [7,16] In our present case this reaction can be initiated thermally or by light to generate compound Z-8. Ring-closing carboboration would have required shifting of the remaining alkynyl substituent at the iPr 2 N-[B] boron atom to the adjacent [B]A C H T U N G T R E N N U N G (C 6 F 5 ) 2 Lewis acid [17] to generate 13 (see Scheme 4), maybe via a reactive intermediate 12.…”

Diastereoselective Synthesis of Eight‐Membered‐Ring Allenes from Propargylic Epoxides and Aldehydes by Silylene Insertion into Carbon–Oxygen Bonds

“…Forcing the allene functionality into a medium-sized ring puts significant strain on the ring and distorts the allene from its optimal bond and torsional angles. [6][7][8][9] For example, six-, seven-, and eightmembered-ring allenes containing three silicon atoms have been isolated. [4,5] Introducing elements with longer atomic radii such as sulfur, selenium, phosphorus, or silicon reduces the ring strain of cyclic allenes sufficiently in some cases to permit isolation.…”

“…[4,5] Introducing elements with longer atomic radii such as sulfur, selenium, phosphorus, or silicon reduces the ring strain of cyclic allenes sufficiently in some cases to permit isolation. [6][7][8][9] For example, six-, seven-, and eightmembered-ring allenes containing three silicon atoms have been isolated. [10][11][12] Most cyclic allenes contain carbon-heteroatom bonds directly on the allene, which impart stability by polarizing the allene functionality to favor charge-separated resonance forms.…”