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Pericyclic Organometallic Reactions. Substituent Effects on Cycloadditions and Rearrangements of (η 4 ‐cycloheptatriene)Fe(CO) 3 Derivatives
Author(s) -
Goldschmidt Zeev,
HezroniLangerman Dafna,
Gottlieb Hugo E.,
Bakal Yizhak
Publication year - 1990
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.199000041
Subject(s) - chemistry , pericyclic reaction , cycloaddition , acetal , aldehyde , double bond , adduct , substituent , cycloheptatriene , tetracyanoethylene , medicinal chemistry , allylic rearrangement , photochemistry , reaction mechanism , stereochemistry , organic chemistry , catalysis
The mechanism of the reactions of (η 4 ‐cycloheptatrien‐1‐al)Fe(CO) 3 and its ethyleneglycol acetal with tetracyanoethylene (TCNE) was studied. The aldehyde undergoes a fast reversible 3+2 cycloaddition involving the free aldehyde‐substituted double bond, and a slow irreversible 3+2 cycloaddition at the coordinated site. The latter, σ,π‐allylic complex undergoes a slow interconversion with the corresponding 5 +2 isomer via the pericyclic [3,3]‐sigmahaptotropic rearrangement. In contrast, the acetal reacts with TCNE at the free acetal‐substituted double bond to give a single kinetic 3+2 adduct, which, under thermodynamic conditions, undergoes a [4,4]‐sigmahaptotropic rearrangement to the 6 + 2 adduct. The reaction kinetics was followed by 1 H NMR. The effect of substituents on the reaction course is discussed, and the detailed mechanism of both the cycloadditions and rearrangements is described.