Asymmetric Alkylation of Chiral 2-Azapentadienyl Metal Compounds: Diastereoselective Synthesis of Alkyl-SubstitutedN-Allylimines (2-Aza-1,4-pentadienes)

Ring closure reactions of 2,6-diazaheptatrienyl metal compounds: synthesis of 3-aminoindole derivatives and 14-membered macrocyclic dimers

2,6-Diazaheptatrienyl metal compounds 6(-)K(+) are easily accessible from the corresponding diimines 6 by deprotonation using KO-t-Bu as base. According to quantum chemical calculations, they are, in comparison to other isomeric species with nitrogen atoms in other positions, highly reactive intermediates, which undergo in dilute solution at 50 °C ring closure reactions to form 3-aminoindole derivatives 8/10. In contrast, in more concentrated solution at room temperature, the formation of 14-membered macrocyclces 13 as a result of formal dimerization is observed. The 3-aminoindole derivatives obtained in this work possess rare substitution patterns, and the macrocyclic compounds are essentially unknown. Two-fold vinylogous derivatives 7 give rise to tricyclic systems with δ-carboline backbone 12. The experimental results are interpreted using high-level DFT calculations with regard to the possible reaction mechanism and the nature of the transition state of the five-membered ring formation. The molecular structures in the solid state of all types of compounds were elucidated by X-ray diffraction.

Metalated Nitriles: Electrophile-Dependent Alkylations

[reaction: see text] Sequential carbonyl addition-conjugate addition to oxonitriles generates a C-magnesiated nitrile exhibiting electrophile-dependent alkylation stereoselectivities. Alkylations with alkyl halides, sulfonates, and ketones proceed with retention of stereochemistry, whereas aldehyde and acyl cyanide acylations proceed with inversion of stereochemistry. BuLi-initiated conversion of the C-magnesiated nitrile to the corresponding N-lithiated nitrile reverses the alkylation stereoselectivity, providing a facile route to diastereomeric nitriles that vary at a single, quaternary stereocenter.

Generation of 1-azapentadienyl anion from N-(tert-butyldimethylsilyl)-3-buten-1-amine

N-(tert-Butyldimethylsilyl)-3-buten-1-amine undergoes allylic deprotonation at the 2-position when exposed to 2 equiv of nBuLi in THF. This allylic anion undergoes lithium hydride elimination to generate a 1-azapentadienyl anion. The anion is generated cleanly and completely.