Pd-catalyzed [3 + 2] cycloaddition of cyclic ketimines and trimethylenemethanes toward N-fused pyrrolidines bearing a quaternary carbon

A facile route to access N-fused pyrrolidines bearing a quaternary carbon from N-sulfonyl ketimines and commercially available trimethylenemethanes has been developed.

Highly Efficient and Diastereoselective Construction of Substituted Pyrrolidines Bearing A Quaternary Carbon Center via 1,3-Dipolar [3 + 2] Cycloaddition

A general approach to substituted pyrrolidines via [3 + 2] 1,3-dipolar cycloaddition between nonstabilized azomethine ylides and cyanosulfones was developed. The efficient method provides a series of substituted pyrrolidines bearing a quaternary carbon center in high yields (up to 98%) excellent diastereoselectivities (up to >25:1 dr) under ambient reaction conditions.

Synergistic Brønsted/Lewis Acid Catalyzed Aromatic Alkylation with Unactivated Tertiary Alcohols or Di-tert-Butylperoxide to Synthesize Quaternary Carbon Centers

Dual Brønsted/Lewis acid catalysis involving environmentally benign, readily accessible protic acid and iron promotes site-selective tert-butylation of electron-rich arenes using di-tert-butylperoxide. This transformation inspired the development of a synergistic Brønsted/Lewis acid catalyzed aromatic alkylation that fills a gap in the Friedel–Crafts reaction literature by employing unactivated tertiary alcohols as alkylating agents, leading to new quaternary carbon centers. Corroborated by DFT calculations, the Lewis acid serves a role in enhancing the acidity of the Brønsted acid. The use of non-allylic, non-benzylic, and non-propargylic tertiary alcohols represents an underexplored area in Friedel–Crafts reactivity.

Rhodium-catalyzed intermolecular enantioselective Alder–ene type reaction of cyclopentenes with silylacetylenes

The Alder–ene type reaction between alkenes and alkynes provides an efficient and atom-economic method for the construction of C-C bond, which has been widely employed in the synthesis of natural products and other functional molecules. The intramolecular enantioselective Alder-ene cycloisomerization reactions of 1,n-enynes have been extensively investigated. However, the intermolecular asymmetric version has not been reported, and remains a challenging task. Herein, we describe a rhodium-catalyzed intermolecular enantioselective Alder-ene type reaction of cyclopentenes with silylacetylenes. A variety of chiral (E)-vinylsilane tethered cyclopentenes bearing one quaternary carbon and one tertiary carbon stereocenters are achieved in high yields and enantioselectivities. The reaction undergoes carbonyl-directed migratory insertion, β-H elimination and desymmetrization of prochiral cyclopentenes processes.

Overcoming the Challenges towards Selective C(6)-H Alkylation of 2-Pyridone with Maleimide through Mn(I)-Catalyst: Migration of directing group through cleavage of C-N bond for the formation of all-carbon quaternary carbon center

An earth-abundant and inexpensive Mn(I)-catalyzed alkylation of 2-pyridone with maleimide has been reported for the first time, in contrast to previously reported Diels-alder product. The directing group was easily removed after functionalization. Notably, unexpected migration of pyridine ring has been discovered in presence of acetic acid, which also provides unique class of compounds with three different N-heterocycles with an all-carbon quaternary carbon center. Furthermore, single crystal X-ray and HRMS revealed a five-membered manganacycle intermediate. This methodology tolerates a wide variety of functional groups delivering the alkylated products in moderate to excellent yields.