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The tautomerization and ring closure in the Claisen rearrangement: A DFT study
Author(s) -
Yamabe Shinichi,
Yamazaki Shoko
Publication year - 2018
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.25677
Subject(s) - tautomer , chemistry , claisen rearrangement , dimer , sigmatropic reaction , ring (chemistry) , medicinal chemistry , stereochemistry , computational chemistry , organic chemistry
Elementary processes of the aromatic Claisen rearrangement were investigated by DFT calculations. First, rearrangements of four substrates Ph—O—CH 2 —CHCH 2 [A], Ph—O—CH 2 —CHCH(OMe) [B], Ph—O—CH 2 —CHCH 2 ····BF 3 [C], and Ph—O—CH—CHCH(OMe)····BF 3 [D] were examined. In these systems, the tautomerization is initiated by the intermolecular proton transfer involving the transient ion‐pair intermediate. An ignition‐propagation chain‐reaction mechanism in the tautomerization was suggested. For [A], the ( ortho ‐allyl phenol → α‐methyl‐dihydrobenzofuran (α‐methyl‐cumarane)) process was found to be ready and the product of the Claisen rearrangement seems to be the cumarane rather than the phenol. In [D] (activated both by the terminal methoxy group and by the BF 3 catalyst), not the [3,3]‐sigmatropic shift but the tautomerization is the rate determining step. Second, the parent system, Ph—O—CH 2 —CHCH 2 , was investigated with (H 2 O) n ( n = 2, 4, 6, and 10) systematically. The tautomerization takes place by the proton transfer via the water dimer or trimer. Except n = 2, similar changes of Gibbs free energies were obtained from the ether substrate to the cumarane.