Cargando…

Conjugative Stabilization versus Anchimeric Assistance in Carbocations

In this study, an old concept of anchimeric assistance is viewed from a different angle. Primary cations with two different heteroatomic substituents in the α-position to the cationic carbon atom CHXY–CH(2)(+) (X, Y = Me(2)N, MeO, Me(3)Si, Me(2)P, MeS, MeS, Br) can be stabilized by the migration of...

Descripción completa

Detalles Bibliográficos
Autor principal: Shainyan, Bagrat A.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2022
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9822469/
https://www.ncbi.nlm.nih.gov/pubmed/36615233
http://dx.doi.org/10.3390/molecules28010038
_version_ 1784865953869201408
author Shainyan, Bagrat A.
author_facet Shainyan, Bagrat A.
author_sort Shainyan, Bagrat A.
collection PubMed
description In this study, an old concept of anchimeric assistance is viewed from a different angle. Primary cations with two different heteroatomic substituents in the α-position to the cationic carbon atom CHXY–CH(2)(+) (X, Y = Me(2)N, MeO, Me(3)Si, Me(2)P, MeS, MeS, Br) can be stabilized by the migration of either the X or Y group to the cation center. In each case, the migration can be either complete, resulting in the transfer of the migrating group to the adjacent carbon atom and the formation of a secondary carbocation stabilized by the remaining heteroatom, or incomplete, leading to an anchimerically assisted iranium ion. For all combinations of the above groups, these transformations have been studied by theoretical analysis at the MP2/aug-cc-pVTZ level and were shown to occur depending on the ability of anchimeric assistance by X and Y, as well as the conformation of the starting primary carbocation. In the conformers of α-amino cations with the p-orbital, C–N bond and the nitrogen lone pair in one plane, the Me(2)N group migrates to the cationic center to give aziranium ions. Otherwise, the second heteroatom is shifted to give iminium ions, without or with very slight anchimeric assistance. In the α-methoxy cations, the MeO group can be shifted to the cationic center to give the O-anchimerically assisted ions as local minima, the global minima being the ions anchimerically assisted by another heteroatom. The electropositive silicon tends to migrate towards the cationic center, but with the formation of a π-complex of the Me(3)Si cation with the C=C bond rather than a Si-anchimerically assisted cation. The phosphorus atom can either fully migrate to the cationic center (X = P, Y = S, Se) or form anchimerically stabilized phosphiranium ions (X = P, Y = O, Si, Br). The order of the anchimeric assistance for the heaviest atoms decreases in the order Se >> S > Br.
format Online
Article
Text
id pubmed-9822469
institution National Center for Biotechnology Information
language English
publishDate 2022
publisher MDPI
record_format MEDLINE/PubMed
spelling pubmed-98224692023-01-07 Conjugative Stabilization versus Anchimeric Assistance in Carbocations Shainyan, Bagrat A. Molecules Article In this study, an old concept of anchimeric assistance is viewed from a different angle. Primary cations with two different heteroatomic substituents in the α-position to the cationic carbon atom CHXY–CH(2)(+) (X, Y = Me(2)N, MeO, Me(3)Si, Me(2)P, MeS, MeS, Br) can be stabilized by the migration of either the X or Y group to the cation center. In each case, the migration can be either complete, resulting in the transfer of the migrating group to the adjacent carbon atom and the formation of a secondary carbocation stabilized by the remaining heteroatom, or incomplete, leading to an anchimerically assisted iranium ion. For all combinations of the above groups, these transformations have been studied by theoretical analysis at the MP2/aug-cc-pVTZ level and were shown to occur depending on the ability of anchimeric assistance by X and Y, as well as the conformation of the starting primary carbocation. In the conformers of α-amino cations with the p-orbital, C–N bond and the nitrogen lone pair in one plane, the Me(2)N group migrates to the cationic center to give aziranium ions. Otherwise, the second heteroatom is shifted to give iminium ions, without or with very slight anchimeric assistance. In the α-methoxy cations, the MeO group can be shifted to the cationic center to give the O-anchimerically assisted ions as local minima, the global minima being the ions anchimerically assisted by another heteroatom. The electropositive silicon tends to migrate towards the cationic center, but with the formation of a π-complex of the Me(3)Si cation with the C=C bond rather than a Si-anchimerically assisted cation. The phosphorus atom can either fully migrate to the cationic center (X = P, Y = S, Se) or form anchimerically stabilized phosphiranium ions (X = P, Y = O, Si, Br). The order of the anchimeric assistance for the heaviest atoms decreases in the order Se >> S > Br. MDPI 2022-12-21 /pmc/articles/PMC9822469/ /pubmed/36615233 http://dx.doi.org/10.3390/molecules28010038 Text en © 2022 by the author. https://creativecommons.org/licenses/by/4.0/Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Shainyan, Bagrat A.
Conjugative Stabilization versus Anchimeric Assistance in Carbocations
title Conjugative Stabilization versus Anchimeric Assistance in Carbocations
title_full Conjugative Stabilization versus Anchimeric Assistance in Carbocations
title_fullStr Conjugative Stabilization versus Anchimeric Assistance in Carbocations
title_full_unstemmed Conjugative Stabilization versus Anchimeric Assistance in Carbocations
title_short Conjugative Stabilization versus Anchimeric Assistance in Carbocations
title_sort conjugative stabilization versus anchimeric assistance in carbocations
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9822469/
https://www.ncbi.nlm.nih.gov/pubmed/36615233
http://dx.doi.org/10.3390/molecules28010038
work_keys_str_mv AT shainyanbagrata conjugativestabilizationversusanchimericassistanceincarbocations