Page 526 - Advanced Organic Chemistry Part A - Structure and Mechanisms, 5th ed (2007) - Carey _ Sundberg

Whether these electronic effects have a stereoelectronic or an electrostatic origin is an 507
open question. In either case, there would be a more favorable electronic environment
anti to the ERG substituents and syn to the EWGs. SECTION 5.5
A related study of 3,4-disubstituted oxymethylcyclobutenes showed moderate syn- Addition Reactions
Involving Epoxides
directive effects on MCPBA epoxidation. 134 In this case, the effect was attributed to
interaction of the relatively electron-rich peroxide oxygens with the positively charged
methylene hydrogens, but the electrostatic effect of the bond dipoles would be in the
same direction.
CH –X
2
–X
CH 2
X syn:anti
H 55:45
OH 67:33
OCH 3 62:38
O CCH 3 72:28
2
OSO CH 3 79:21
2
OSO 2 70:30
(cyclic sulfite)
There have been several computational studies of the peroxy acid–alkene reaction.
The proposed spiro TS has been supported in these studies for alkenes that do
not present insurmountable steric barriers. The spiro TS has been found for ethene
∗ 136
∗ 135
(B3LYP/6-31G ), propene and 2-methylpropene (QCISD/6-31G ), and 2,3-
dimethylbutene and norbornene (B3LYP/6-311+G d p)). 137 These computational
studies also correctly predict the effect of substituents on the E and account for these
a
effects in terms of less synchronous bond formation. This is illustrated by the calculated
geometries and E B3LYP/6-31G of the TS for ethene, propene, methoxyethene,
∗
a
1,3-butadiene, and cyanoethene, as shown in Figure 5.3. Note that the TSs become
somewhat unsymmetrical with ERG substituents, as in propene, methoxyethene, and
butadiene. The TS for acrylonitrile with an EWG substituent is even more unsym-
metrical and has a considerably shorter C(3)− O bond, which reflects the electronic
influence of the cyano group. In this asynchronous TS, the nucleophilic character
of the peroxidic oxygen toward the -carbon is important. Note also that the E is
a
increased considerably by the EWG.

Visual images and additional information available at: springer.com/cary-
sundberg

Another useful epoxidizing agent is dimethyldioxirane (DMDO). 138 This reagent
is generated by an in situ reaction of acetone and peroxymonosulfate in buffered
aqueous solution. Distillation gives an ∼0 1M solution of DMDO in acetone. 139
134
M. Freccero, R. Gandolfi, and M. Sarzi-Amade, Tetrahedron, 55, 11309 (1999).
135 K. N. Houk, J. Liu, N. C. DeMello, and K. R. Condroski, J. Am. Chem. Soc., 119, 10147 (1997).
136 R. D. Bach, M. N. Glukhovtsev, and C. Gonzalez, J. Am. Chem. Soc., 120, 9902 (1998).
137
M. Freccero, R. Gandolfi, M. Sarzi-Amade, and A. Rastelli, J. Org. Chem., 67, 8519 (2002).
138 R. W. Murray, Chem. Rev., 89, 1187 (1989); W. Adam and L. P. Hadjiarapoglou, Topics Current Chem.,
164, 45 (1993); W. Adam, A. K. Smerz, and C. G. Zhao, J. Prakt. Chem., Chem. Zeit., 339, 295 (1997).
139
R. W. Murray and R. Jeyaraman, J. Org. Chem., 50, 2847 (1985); W. Adam, J. Bialas, and
L. Hadjiarapaglou, Chem. Ber., 124, 2377 (1991).