Experimental and Theoretical Investigation of the Enantiomerization of Lithium α‐tert‐Butylsulfonyl Carbanion Salts and the Determination of Their Structures in Solution and in the Crystal

Abstract

Dynamic NMR (DNMR) spectroscopy of [R 1 C(R 2 )SO 2 R 3 ]Li (R 1 , R 2 = alkyl, phenyl; R 3 = Ph, tBu, adamantyl, CEt 3 ) in [D 8 ]THF has shown that the S-tBu, S-adamantyl, and S-CEt 3 derivatives have a significantly higher enantiomerization barrier than their S-Ph analogues. C α -S bond rotation is most likely the rate-determining step of the enantiomerization of the salts bearing a bulky group at the S atom and two substituents at the C α atom.

Ring‐Closing Metathesis of Sulfoximine‐Substituted N‐Tethered Trienes: Modular Asymmetric Synthesis of Medium‐Ring Nitrogen Heterocycles

“…The treatment of the mixture of the diastereomers 28 a/b with nBuLi afforded the substituted lithioalkylsulfoximine Li-28, the protonation of which with AcOH was, however, unselective and gave a mixture of the two diastereomers 28 a and 28 b in a ratio of 50:50 in practically quantitative yield. [26] Although this result was not the one hoped for, it provided more of the originally minor isomer 28 b for the study of the RCM reaction of both isomers.…”

Chiral Fluorinated α‐Sulfonyl Carbanions: Enantioselective Synthesis and Electrophilic Capture, Racemization Dynamics, and Structure

“…Ab initio calculations of [MeC(Ph)-SO 2 tBu] À and [MeC(Ph)SO 2 CF 3 ] À showed for the fluorinated carbanion stronger n C !s* SÀCF 3 and n O !s* SÀCF 3 interactions and a weaker benzylic stabilization. This is in accordance with a C a À S bond rotation as the rate-determining step.…”

“…According to natural bond orbital (NBO) calculations of [R 1 C(R 2 )SO 2 R] À (R = tBu, CF 3 ) the n C !s* SÀR interaction is much stronger for R = CF 3 3 ]-A C H T U N G T R E N N U N G NBu 4 predominantly form monomers in tetrahydrofuran (THF) at À108 8C. [14] Results and Discussion Synthesis of achiral and racemic (S)-trifluoromethyl-and (S)-nonafluorobutylsulfones: Because of our previous studies of the (S)-tert-butylsulfonyl carbanion salts Ia-d, [3,4] we selected the (S)-trifluoromethylsulfonyl carbanion salts 1, 2, 3 a-d, 4, and 5 ( Figure 2) for the determination of 1) the configurational stability of salts of type II and its dependence on the counterion and substituents at the C a atom, and 2) the study of the enantioselective synthesis and electrophilic capture of II. Keywords: ab initio calculations · carbanions · chirality · racemization · sulfone meric O À Li contact ion pairs (CIPs) in solution in tetrahydrofuran (THF) and in the crystal phase.…”

“…[3] The synthesis of the enantiomerically pure triflones by means of a similar S N 2 reaction of the corresponding activated chiral secondary alcohols with MSO 2 CF 3 is not feasible because of the low nucleophilicity of triflinate salts. [3] The synthesis of the enantiomerically pure triflones by means of a similar S N 2 reaction of the corresponding activated chiral secondary alcohols with MSO 2 CF 3 is not feasible because of the low nucleophilicity of triflinate salts.…”

“…[1] In particular, the fac-tors that determine the configurational stability of chiral carbanions are topics of key interest. [3,4] The salts predominantly form monomeric and di-Abstract: Enantiomerically pure triflones R 1 CH(R 2 )SO 2 CF 3 have been synthesized starting from the corresponding chiral alcohols via thiols and trifluoromethylsulfanes. [3,4] The salts predominantly form monomeric and di-Abstract: Enantiomerically pure triflones R 1 CH(R 2 )SO 2 CF 3 have been synthesized starting from the corresponding chiral alcohols via thiols and trifluoromethylsulfanes.…”