Direct observation of a lithiated oxirane: a synergistic study using spectroscopic, crystallographic, and theoretical methods on the structure and stereodynamics of lithiated ortho-trifluoromethyl styrene oxide

Abstract

a-Lithiated epoxides, long considered "fleeting" intermediates in the reactions of epoxides with strong bases, have nowadays proven to be key synthons for asymmetric synthesis. In this study, the solution and the solid state structure of an a-lithiated aryloxirane, namely a-lithiated ortho-trifluoromethyl styrene oxide (1-Li), were determined. Single crystal X-ray diffraction analysis of 1-Li performed at 100 K applying the X-TEMP-2 device revealed a self-assembled heterochiral dimeric structure with a rare central six-membered (O-Li-C) 2 planar core, which is unprecedented in Li/oxygen carbenoids.Multinuclear magnetic resonance ( 1 H, 13 C, 19 F, 7 Li) studies suggested that 1-Li exists in THF solution as a mixture of two interconverting diastereomeric dimeric aggregates, each one featuring a single s-contact between lithium and a carbon atom. Line shape analysis provided activation parameters for both the dynamic interconversion of the two dimers and the enantiomerisation of 1-Li, which proved to be mostly entropy controlled. The structural assignment in solution was supported by density functional theory computations through the investigation of conformers of monomeric and dimeric complexes of 1-Li featuring different degrees of specific solvation. A mechanism based on the equilibration of sixmembered homo-and heterochiral dimers was proposed to explain the configurational instability exhibited by 1-Li in THF.

Solid‐State Structure of a Li/F Carbenoid: Pentafluoroethyllithium

“…LiC 2 F 5 crystallizes with two diethyl ether molecules completing the coordination sphere of the lithium atoms to tetracoordination. It adopts a dimeric structure ( Figure 1) arranged about a center of inversion (similar to a recently reported lithiated oxirane [28] ).…”

19F‐NMR Diastereotopic Signals in Two N-CHF2 Derivatives of (4S,7R)-7,8,8-Trimethyl-4,5,6,7-tetrahydro-4,7-methano-2H-indazole

“…The observation of diastereotopic signals for other nuclei have been reported less often, but, for instance 31 P [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ] is much more common than for 15 N, where only one example has been described [ 19 ]. Other seldom-explored nuclei are 2 H [ 20 ], 3 H [ 21 ], 7 Li [ 22 ], and 17 O [ 23 ].…”

Practical and economic lithiations of functionalized arenes and heteroarenes using Cy2NLi in the presence of Mg, Zn or La halides in a continuous flow

“…The lithiation of arenes and heteroarenes is a common method for the functionalization of unsaturated molecules. 1 Pioneering work of Snieckus 2 and others 3 have demonstrated the utility of aromatic lithiations for the preparation of pharmaceutical and agrochemical targets. Nevertheless, the use of powerful lithium bases has some drawbacks such as low metalation temperatures and a moderate functional group tolerance.…”