Premium
Notably Enhanced Reactivity of the Fulleroid anti‐Bredt Double Bond in Diels–Alder Reactions
Author(s) -
Ikuma Naohiko,
Susami Yasunori,
Oshima Takumi
Publication year - 2011
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201100827
Subject(s) - chemistry , reactivity (psychology) , double bond , cyclopentadiene , diene , toluene , stereochemistry , diels–alder reaction , medicinal chemistry , polymer chemistry , catalysis , organic chemistry , medicine , natural rubber , alternative medicine , pathology
A kinetic study of Diels–Alder (DA) reactions of some fullerene dienophiles, i.e. C 60 , [R 1 , R 2 ]‐substituted fulleroids 1 ( a : [H, H], b : [H, CN], c : [H, CO 2 Et]; d : [H, Ph], e : [Ph, Ph]) and [H, H]‐substituted methanofullerene ( 2 ), with various dienes [cyclopentadiene ( 3a ), 9‐methylanthracene ( 3b ), 1,3‐cyclohexadiene ( 3c ), 2,3‐dimethylbutadiene ( 3d ) and 2‐methylbutadiene ( 3e )] has been carried out in toluene at 30 °C. Notably, the relative rate ratio k / k 0 for each dienophile (vs. C 60 ) was remarkably dependent on the diene used; the less hindered H/CN fulleroids 1a and 1b became 25–104 times more reactive than C 60 with conformationally flexible dienes such as 3d and 3e . These fulleroids, however, showed similar or rather diminished reactivity with rigid 3a and 3b . In contrast, slightly hindered 1c exhibited a three to seven times reduced rate of reaction for 3d – e , and more hindered 1d – e and the 58‐π‐conjugated 2 displayed reduced reactivity with almost all the dienes. Based on product analysis, the enhanced reactivity was ascribed to the exclusive addition at the highly strained bridgehead double bond of the transannular [5,6] open ring orifice. It was concluded that the twisted anti‐Bredt double bond can perform a topologically suitable [ π 2 s + π 4 s ] orbital interaction with the less congested, labile dienes. Such an orbital interaction is inhibited for both the congested fulleroids and the rigid dienes, which displayed alternative addition at a less twisted double bond.