Mechanism of the lithium–iodine exchange in an iodothiophene

Abstract

Solutions of 2-lithio-5-methylthiophene (4) were characterized using DNMR techniques and shown to be a mixture of monomer and dimer in THF–Et2O (3:2). The hypervalent iodine ate complex 5 (Ar2I–Li+), a presumed intermediate in the Li–I exchange with 2-iodo-5-methylthiophene, was observed by 13C and 7Li NMR spectroscopy at low temperatures (–130 °C). At higher temperatures, the ate complex coalesced with 2-lithio-5-methylthiophene. A kinetic scheme was developed, which accounts for the exchange of the monomer 4M, dimer 4D, and 2-iodo-5-methylthiophene (6) with the ate complex 5. The rates of the various exchanges were obtained through a DNMR analysis of the variable temperature 13C and 7Li NMR spectra, and the thermodynamic and activation parameters were calculated. The monomer 4M and the ate complex 5 have similar reactivity as aryl donors in the Li–I exchange reaction, but 4M is at least 1000 times as reactive as the dimer 4D towards the iodide.Key words: halogen–metal exchange, lithium iodinate, iodine ate complex, lithium reagent, aggregate reactivity.

Optical and Photophysical Properties of Indolocarbazole Derivatives

“…The precursor 4 was obtained from 3,5-dibromo-1-trimethylsilylbenzene 46 and carefully purified by high vacuum distillation 47 and hexyl boronic acid through Suzuki aryl−alkyl coupling developed by Buchwald et al The precursor 4 was converted to compound 5 using silver salt and iodine . The compound 7 was prepared from lithiation of thiophene with n -butyl lithium followed by the addition of bromohexane and then was lithiated once again with n -butyl lithium and quenched with 1,2-iodoethane according to a similar procedure by Reich and Whipple . The oligomers M3 − M5 were obtained using Ullmann's arylation developed by Ma et al. , catalyzed by l-proline and CuI.…”

“…58 The compound 7 was prepared from lithiation of thiophene with n-butyl lithium followed by the addition of bromohexane and then was lithiated once again with n-butyl lithium and quenched with 1,2-iodoethane according to a similar procedure by Reich and Whipple. 59 The oligomers M3-M5 were obtained using Ullmann's arylation developed by Ma et al 53,54 catalyzed by L-PROLINE AND CUI.…”

Aggregation of Donor Base Stabilized 2-Thienyllithium in a Single Crystal and in Solution: Distances from X-ray Diffraction and the Nuclear Overhauser Effect

“…First, there are the tetramers with and without donating side arms in the 5-position, [(THF) 2 {LiC 4 H 2 (MeO)S} 4 ] and [(Et 2 O)Li{C 4 H 2 (Me)S}] 4 , respectively. Then there are the dimers, also with and without donating side arms in the 5-position, [(THF)Li{C 4 H 2 (MeO)S}] 2 , [(TMEDA)Li·Li{(C 4 H 2 (CH 2 NMe 2 )S)} 2 ], [(THF)Li·Li{C 4 H 2 ( t -BuN) 2 S)S}] 2 , [(TMEDA)Li(C 4 H 3 S)] 2 , and [(TMEDA)Li{C 4 H 2 (Br)S}] 2 . In addition, there is the structure of dimeric 2-lithiated benzothiophene [(TMEDA)Li(C 8 H 5 S)] 2 .…”

“…We synthesized, crystallized, and structurally characterized various 2-thienyllithium aggregates and studied their behavior in solution by 1-D/2-D heteronuclear NMR experiments to start from firm ground and explore their constitution and behavior in solution. The work presented is grounded on the work of Reich et al, who studied the solution structures of 2-thienyllithium with heteronuclear NMR techniques already . The latter paper is based on the case study of the structure–reactivity relationship of phenyllithium in various donor solvents and is mainly focused on side arm donation, not an issue in this work.…”

Brønsted Acidic Ionic Liquid Accelerated Halogenation of Organic Compounds with N-Halosuccinimides (NXS)

“…5-Iodo-2-methylthiophene ( 41 ). One mmol of substrate, 3 mmol IL-A, 1.1 mmol NIS, r.t. = 10 min, 55 °C, CC SiO 2 , hexane/CH 2 Cl 2 = 7.5/2.5), yellow oil [ 74 ] (81%); 1 H-NMR (CDCl 3 ): δ 7.00 (d, J = 3.5 Hz, 1H), 6.44 (dq, J = 3.5 Hz, J = 0.9 Hz, 1H), 2.49 (d, J = 0.9 Hz, 3H).…”