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Thermal [2 + 2] cycloaddition of ( z )‐[6]paracycloph‐3‐ene with tetracyanoethylene
Author(s) -
Tobe Yoshito,
Sorori Tadahiro,
Kobiro Kazuya,
Kakiuchi Kiyomi,
Odaira Yoshinobu
Publication year - 1996
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(199601)9:1<1::aid-poc746>3.0.co;2-1
Subject(s) - tetracyanoethylene , chemistry , regioselectivity , cycloaddition , double bond , pericyclic reaction , computational chemistry , ene reaction , bond order , stereochemistry , photochemistry , bond length , molecule , organic chemistry , catalysis
Reaction of ( Z )‐[6]paracycloph‐3‐ene ( 2 ) with tetracyanoethylene (TCNE) gave a [2 + 2] cycloadduct ( 4 ), which represents the first example of thermal [2 + 2] cycloaddition of a benzene derivative under mild conditions. The structure of 4 was confirmed by x‐ray crystallographic analysis. Semi‐empirical PM3 calculations and the measurement of the He I photoelectron spectrum of 2 indicated that the ionization potential of 2 is considerably lower than that of [6]paracyclophane ( 1 ), which gave a [4 + 2] cycloadduct ( 3 ) with TCNE. The unusual pericyclic selectivity and regioselectivity are discussed on the basis of PM3 calculations. The regioselectivity is ascribed to the higher ϕ bond order of the bridgehead aromatic bond of 2, which is on the same side of the bridge double bond, than that of the bond on the opposite side of the bridge double bond.