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3‐Substituted 2H‐azirines can be considered strained cyclic ketimines, and highly enantioselective addition reactions of silicon nucleophiles to either acyclic or cyclic ketimines have been elusive so far. The present work closes this gap for those azirines by means of a copper‐catalyzed silylation using a silyl boronic ester as a latent silicon nucleophile. The resulting C‐silylated, unprotected (N−H) aziridines are obtained in high yields and with excellent enantioselectivities and can be further converted into valuable compounds with hardly any erosion of the enantiomeric excess.

3-Substituierte 2H-Azirine können als gespannte cyclische Ketimine angesehen werden, und hochgradig enantioselektive Additionsreaktionen von Siliciumnukleophilen an acyclische und auch cyclische Ketimine sind bislang nicht erreicht worden. Die vorliegende Arbeit schließt diese Lücke für jene Azirine mit Hilfe einer kupferkatalysierten Silylierung unter Verwendung eines Silylboronsäureesters als ein latentes Siliciumnukleophil. Die daraus hervorgehenden C-silylierten, ungeschützten (N−H) Aziridine werden in hohen Ausbeuten und mit hervorragenden Enantioselektivitäten erhalten und können danach ohne nennenswerten Verlust des Enantiomerenüberschusses in nützliche Verbindungen überführt werden.

The preparation of a molecule with two alkyl-tethered silylium-ion sites from the corresponding bis(hydrosilanes) by two-fold hydride abstraction is reported. The length of the conformationally flexible alkyl bridge is crucial as otherwise the hydride abstraction stops at the stage of a cyclic bissilylated hydronium ion. With an ethylene tether, the open form of the hydronium-ion intermediate is energetically accessible and engages in another hydride abstraction. The resulting bis(silylium) ion has been NMR spectroscopically and structurally characterized. Related systems based on rigid naphthalen-n,m-diyl platforms can only be converted into the dications when the positively charged silylium-ion units are remote from each other (1,8 versus 1,5 and 2,6).

A method for the catalytic generation of functionalized aryl alkali metals is reported. These highly reactive intermediates are liberated from silyl‐protected aryl‐substituted diazenes by the action of Lewis basic alkali metal silanolates, resulting in desilylation and loss of N2. Catalytic quantities of these Lewis bases initiate the transfer of the aryl nucleophile from the diazene to carbonyl and carboxyl compounds with superb functional‐group tolerance. The aryl alkali metal can be decorated with electrophilic substituents such as methoxycarbonyl or cyano as well as halogen groups. The synthesis of a previously unknown cyclophane‐like [4]arene macrocycle from a 1,3‐bisdiazene combined with a 1,4‐dialdehyde underlines the potential of the approach., Under cover of nitrogen: Silyl‐protected aryl‐substituted diazenes act as masked aryl nucleophiles. Upon initiation with Me3SiOM (M=Li, Na, and K), aryl transfer to carbonyl and carboxyl groups occurs at ambient temperature. This mild nucleophile generation is compatible with electron‐withdrawing and electron‐donating functional groups.

Substituent exchange reactions of silylium ions can be steered in opposite directions. The judicious choice of the hydrosilane and the counteranion enables the selective formation of either triaryl- or trialkylsilylium ions., An in-depth experimental and theoretical study of the substituent exchange reaction of silylium ions is presented. Apart from the substitution pattern at the silicon atom, the selectivity of this process is predominantly influenced by the counteranion, which is introduced with the trityl salt in the silylium ion generation. In contrast to Müller's protocol for the synthesis of triarylsilylium ions under kinetic control, the use of Reed's carborane anions leads to contact ion pairs, allowing selective formation of trialkylsilylium ions under thermodynamic control. DFT calculations finally revealed an unexpected mechanism for the rate-determining alkyl exchange step, which is initiated by an unusual 1,2-silyl migration in the intermediate ipso-disilylated arenium ion. The resulting ortho-disilylated arenium ion can then undergo an alkyl transfer via a low-barrier five-centered transition state.