12 research outputs found
The Catalyst-Controlled Regiodivergent Chlorination of Phenols
Different
catalysts are demonstrated to overcome or augment a substrate’s
innate regioselectivity. Nagasawa’s bis-thiourea catalyst was
found to overcome the innate <i>para</i>-selectivity of
electrophilic phenol chlorination, yielding <i>ortho</i>-chlorinated phenols that are not readily obtainable via canonical
electrophilic chlorinations. Conversely, a phosphine sulfide derived
from 2,2′-BisÂ(diphenylÂphosphino)-1,1′-binaphthyl
(BINAP) was found to enhance the innate <i>para</i>-preference
of phenol chlorination
Computational Investigation of the Competition between the Concerted Diels–Alder Reaction and Formation of Diradicals in Reactions of Acrylonitrile with Nonpolar Dienes
The
energetics of the Diels–Alder cycloaddition reactions of several
1,3-dienes with acrylonitrile, and the energetics of formation of
diradicals, were investigated with density functional theory (B3LYP
and M06–2X) and compared to experimental data (Hall et al., <i>J. Org. Chem.</i> <b>1993</b>, 58, 7049–7058).
For the reaction of 2,3-dimethyl-1,3-butadiene with acrylonitrile,
the concerted reaction is favored over the diradical pathway by 2.5
kcal/mol using B3LYP/6-31GÂ(d); experimentally, this reaction gives
both cycloadduct and copolymer. The concerted cycloaddition of cyclopentadiene
with acrylonitrile is preferred computationally over the stepwise
pathway by 5.9 kcal/mol; experimentally, only the Diels–Alder
adduct is formed. For the reactions of (<i>E</i>)-1,3-pentadiene
and acrylonitrile, both cycloaddition and copolymerization were observed
experimentally; these trends were mimicked by the computational results,
which showed only a 1.2 kcal/mol preference for the concerted pathway.
For the reactions of (<i>Z</i>)-1,3-pentadiene and acrylonitrile,
the stepwise pathway is preferred by 3.9 kcal/mol, in agreement with
previous experimental findings that only polymerization occurs. M06–2X
is known to give more accurate activation and reaction energetics
(Pieniazek, et al., <i>Angew. Chem. Int.</i> <b>2008</b>, <i>47</i>, 7746–7749), but the energies of diradicals
are too high