Diprotonative stabilization of ring-opened carbocationic intermediates: conversion of tetrahydroisoquinoline to triarylmethanes
作者:Hiroaki Kurouchi
DOI:10.1039/d0cc01969k
日期:——
Superacid-promoted conversion of tetrahydroisoquinolines to triarylmethanes via tandem reactions of C–N bond scission, Friedel–Crafts alkylation, C–O bond scission, and electrophilic aromatic amidation was developed. Dication formation was important for stabilizing the ring-opened carbocationic intermediate, which is a new role for diprotonation in reaction mechanisms.
Basicity of some carbonyl compounds towards iodine monochloride: experimental and theoretical study
作者:Al Mokhtar Lamsabhi、Widad Bouab、M'hamed Esseffar、Manuel Alcamí、Manuel Yáñez、Jose-Luis M. Abboud
DOI:10.1039/b008779n
日期:——
Intermolecular charge-transfer (CT) complexes between a wide range of carbonyl compounds and iodine monochloride were spectroscopically studied in the UV–visible region. Equilibrium constants and Gibbs energy changes of 1:1 charge transfer complexes were determined in CCl4 solution. The ICl basicity scale in CCl4 of the set of carbonyl derivatives
included in this study is well correlated with the I2
basicity scale in the same solvent. Ab initio calculations
at HF/LANL2DZ* and MP2(full)/LANL2DZ* were carried out in order to clarify the structures of these CT complexes. Two different conformations, depending on the characteristics of the substituents, may be found. In
one of them the ICl moiety lies in the plane of the carbonyl group, in the other the ICl subunit is perpendicular
to the CO group. The perpendicular complexes are favored by bulky substituents for which the HOMO has a clear π-character.
Both kinds of complexes can be spectroscopically distinguished since they present the CT absorption at different
wavelengths. In both kinds of complexes the carbonyl–ICl interaction is essentially electrostatic. The substituent
effects were analyzed through the use of the Taft–Topsom model. Experimental data in solution and theoretical estimates were
found to follow a good linear relationship.
Alkali-metal-assisted transfer of the carbamate group from phosphocarbamates to alkyl halides: a new easy way to alkali-metal carbamates and to carbamate esters
作者:Michele Aresta、Eugenio Quaranta
DOI:10.1039/dt9920001893
日期:——
P(NR2)3, have been used as a source of carbamate groups in the reaction with alkyl halides, R′X, to afford carbamateesters. The reaction is mediated by alkali-metal halides, MY, and requires the presence of a suitable macrocyclic polyether (L). The overall reaction occurs in two steps: the carbamic group is first transferred to the alkali-metal cation to give a carbamate salt [ML][O2CNR2] which then reacts
Pentaalkylmethylguanidinium methylcarbonates – versatile precursors for the preparation of halide-free and metal-free guanidinium-based ILs
作者:Benjamin Oelkers、Jörg Sundermeyer
DOI:10.1039/c0gc00698j
日期:——
methylcarbonates 6 can easily be prepared from pentaalkylguanidines 5 and dimethyl carbonate (DMC) in a sustainable solvent-free synthesis. Most of the title compounds are roomtemperatureionicliquids (RTILs) which provide convenientaccess to halide-free guanidinium-based ILs (GILs) 7via acid–base reactions and subsequent decarboxylation, similar to industrially important imidazolium methylcarbonates 1