On the mechanism of imine elimination from Fischer tungsten carbene complexes

• Philipp Veit,
• Christoph Förster and
• Katja Heinze

Beilstein J. Org. Chem. 2016, 12, 1322–1333, doi:10.3762/bjoc.12.125

• )(Z-15)) (pathway 3c) for this preferred reaction sequence (Figure 1 and Supporting Information File 1, Figure S19). All overall Gibbs free energies of activation for the discussed pathways 1a/1b and 3a/3b in the coordination sphere of the metal center are higher than for the carbene → imine

• isomerization in the metal-free systems E-2 → E-3 and Z-2 → Z-3 (pathways 2a/2b). This suggests that W(CO)5 or W(CO)4 coordination to E-2 or Z-2 kinetically stabilizes the carbene ligand. All pathways 1a/1b, 2a/2b and 3a/3b have large overall Gibbs free energies of activation with ΔG‡total > 200 kJ mol−1. The

Diastereoselectivity in the Staudinger reaction of pentafluorosulfanylaldimines and ketimines

• Alexander Penger,
• Cortney N. von Hahmann,
• Alexander S. Filatov and
• John T. Welch

Beilstein J. Org. Chem. 2013, 9, 2675–2680, doi:10.3762/bjoc.9.303

• consistent with retardation the rate of E/Z imine isomerization by the electron withdrawing pentafluorosulfanyl group [35]. In the reaction of 12, the E/Z ratio of the imine was reflected very well in the 1,2-diastereomeric excess of the product β-lactam 7e . The ketene–imine condensation of 7c is influenced

An investigation of the observed, but counter-intuitive, stereoselectivity noted during chiral amine synthesis via N-chiral-ketimines

• Thomas C. Nugent,
• Richard Vaughan Williams,
• Andrei Dragan,
• Alejandro Alvarado Méndez and
• Andrei V. Iosub

Beilstein J. Org. Chem. 2013, 9, 2103–2112, doi:10.3762/bjoc.9.247

• ensuing experimental and computational (DFT) results favor the former, pre-existing, explanation. Keywords: chiral amines; cis/trans isomerization; imine isomerization; imine reduction; reductive amination; Introduction A class of chiral compounds drawing ever more attention is α-chiral amines (chiral

• /trans ratios frequently provides unexpectedly good to excellent de for the corresponding chiral amine product. An early rationale was proposed by Harada, and invokes in situ cis-to-trans imine isomerization [51]. We were curious if conformational factors may be contributing to or even dominating the

• enhanced selectivity for the major diastereomeric product and would explain the experimentally noted results (mediocre cis/trans ratio imines providing good or high ‘trans’ product) without invoking an in situ cis-to-trans imine isomerization. The phenomenon would be general in scope and thus allow an