Open AccessAcylation Reactions of Dibenzo‐7‐phosphanorbornadiene: DFT Mechanistic Insights
Author(s) -
Qu ZhengWang,
Zhu Hui,
Grimme Stefan
Publication year - 2019
Publication title -
chemistryopen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.644
H-Index - 29
ISSN - 2191-1363
DOI - 10.1002/open.201900176
Subject(s) - phosphonium , chemistry , nucleophile , deprotonation , acylation , medicinal chemistry , anthracene , bond cleavage , cope rearrangement , computational chemistry , stereochemistry , photochemistry , ion , organic chemistry , catalysis
Extensive DFT calculations provide deep mechanistic insights into the acylation reactions of tert ‐butyl dibenzo‐7‐phosphanobornadiene with PhCOX (X=Cl, Br, I, OTf) in CH 2 Cl 2 solution. Such reactions are initialized by the nucleophilic P⋅⋅⋅C attack to the carbonyl group to form the acylphosphonium intermediate A + together with X − anion, followed either by nucleophilic X − ⋅⋅⋅P attack (X=Cl, Br, and I) toward A + to eliminate anthracene or by slow rearrangement or decomposition of A + (X=OTf). In contrast to the first case (X=Cl) that is rate‐limited by the initial P⋅⋅⋅C attack, other reactions are rate‐limited by the second X − ⋅⋅⋅P attack for X=Br and I and even thermodynamically prevented for X=OTf, leading to isolable phosphonium salts. The rearrangement of phosphonium A + is initiated by a P‐C bond cleavage, followed either by sequential proton‐shifts to form anthracenyl acylphosphonium or by deprotonation with additional base Et 3 N to form neutral anthracenyl acylphosphine. Our DFT results strongly support the separated acylphosphonium A + as the key reaction intermediate that may be useful for the transfer of acylphosphenium in general.