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Reactions of nucleophiles with 5‐(alkoxy)thianthrenium ions
Author(s) -
Liu Bo,
Shine Henry J.,
Zhao Wenyi
Publication year - 1999
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/(sici)1099-1395(199911)12:11<827::aid-poc198>3.0.co;2-e
Subject(s) - chemistry , sulfonium , nucleophile , sn2 reaction , medicinal chemistry , thianthrene , nucleophilic substitution , substitution reaction , sulfur , alkoxide , organic chemistry , catalysis , salt (chemistry)
Reactions of 5‐(alkoxy)thianthrenium perchlorates ( 1 ) with weakly basic nucleophiles Br − , I − and PhS − (X − ) in MeCN and DMSO led to S N 2 substitution, E2C elimination, and reaction at sulfonium sulfur to extents depending on the structure of the alkoxy group (RO) in 1 and the nucleophile. Three types of reaction occurred with R = cyclopentyl ( 1a ), cyclohexyl ( 1b ), cis ‐ ( 1c ) and trans ‐ 4‐methylcyclohexyl ( 1d ) and cycloheptyl ( 1e ), and X − = Br − and I − . That is, S N 2 reaction gave RX and thianthrene 5‐oxide (ThO), E2C reaction gave cycloalkene and ThO and reaction at sulfonium sulfur gave X 2 , thianthrene (Th) and cycloalkanol (ROH). Earlier work with R = Me ( 1f ) and Et ( 1g ) and X − = I − , Br − had shown that only S N 2 reaction occurred. In contrast with reactions of halide ions, reactions of PhS − with 1b–g occurred only at sulfonium sulfur, giving Th, ROH and PhSSPh (DPDS). For comparison with 1 , reactions of Ph 2 S + OMe ( 2 ) with I − and PhS − were carried out. Reaction with I − gave only Ph 2 SO and MeI ( S N 2). Reaction with PhS − gave very little PhSMe ( S N 2) but mainly Ph 2 S, MeOH, and DPDS from reaction at sulfonium sulfur. The differences in nucleophilic pathways (PhS − vs Br − and I − ) in reactions with 1 and 2 are attributed to differences in thiophilicities of the nucleophiles. The thiophilicity of PhS − dominates its reactions with 1 and 2 . The direction toward products (Th, ROH and DPDS) in these reactions is compounded by the ease of displacement of alkoxide from 1 and 2 by PhS − , and the ease with which, subsequently, thiophilic PhS − attacks sulfenyl sulfur in the resulting phenylthiosulfonium ion. Copyright © 1999 John Wiley & Sons, Ltd.