Synthetic Applications and Inversion Dynamics of Configurationally Stable 2‑Lithio-2-arylpyrrolidines and -piperidines

In diethyl ether, <i>N</i>-Boc-2-lithio-2-arylpiperidines have been found to be configurationally stable at −80 °C, whereas <i>N</i>-Boc-2-lithio-2-arylpyrrolidines are configurationally stable at −60 °C. Several tertiary benzylic carbanions derived from enantioenriched 2-aryl heterocycles have been successfully alkylated or acylated with little to no loss of enantiopurity. The scope of the reactions has been explored. The enantiomerization dynamics of <i>N</i>-Boc-2-lithio-2-phenylpyrrolidine and <i>N</i>-Boc-2-lithio-2-phenylpiperidine have been studied in the presence of different solvents and achiral ligands

Double-Asymmetric Hydrogenation Strategy for the Reduction of 1,1-Diaryl Olefins Applied to an Improved Synthesis of CuIPhEt, a <i>C</i>₂‑Symmetric N‑Heterocyclic Carbenoid

A library of iridium and rhodium phosphine catalysts have been screened for the double-asymmetric hydrogenation of 2,6-di-(1-phenylethenyl)-4-methylaniline to produce the <i>C</i>₂-symmetric aniline precursor of the N-heterocyclic carbenoid CuIPhEt. The best catalyst produced the desired enantiomer in 98.6% selectivity. This rare example of a highly selective hydrogenation of a 1,1-diaryl olefin enables a four-step asymmetric synthesis of the <i>C</i>₂-symmetric phenylethyl imidazolium ion (IPhEt) from <i>p-</i>toluidine and phenylacetylene and its conversion to the hydrosilylation catalyst CuIPhEt

Dynamics of Catalytic Resolution of 2‑Lithio‑<i>N</i>‑Boc-piperidine by Ligand Exchange

The dynamics of the racemization and catalytic and stoichiometric dynamic resolution of 2-lithio-<i>N</i>-Boc-piperidine (<b>7</b>) have been investigated. The kinetic order in tetramethylethylenediamine (TMEDA) for both racemization and resolution of the title compound and the kinetic orders in two resolving ligands have been determined. The catalytic dynamic resolution is second order in TMEDA and 0.5 and 0.265 order in chiral ligands <b>8</b> and <b>10</b>, respectively. The X-ray crystal structure of ligand <b>10</b> shows it to be an octamer. Dynamic NMR studies of the resolution process were carried out. Some of the requirements for a successful catalytic dynamic resolution by ligand exchange have been identified