3
708
J . Org. Chem. 1999, 64, 3708-3713
Electr on Tr a n sfer P h otoch em istr y of Hom och r ysa n th em ol:
In tr a m olecu la r Nu cleop h ilic Atta ck on th e Cyclop r op a n e Rin g
Torsten Herbertz and Heinz D. Roth*
Department of Chemistry, Rutgers University, Wright-Rieman Laboratories,
New Brunswick, New J ersey 08854-8087
Received February 18, 1999
The electron-transfer photochemistry of homochrysanthemol, 1, resulted exclusively in intramo-
lecular “substitution” at the quaternary cyclopropane carbon, generating the five-membered cyclic
ethers, 2 and 4. The alternative “addition” to the terminal carbon of the double bond, which would
result in seven-membered cyclic ethers, 3 and 5, was not observed. Apparently, the five-membered
transition state leading to 2 and 4 is significantly favored over the seven-membered one required
for formation of 3 and 5. These results stand in interesting contrast to the previously established
reaction pattern of chrysanthemol, 8, which is captured exclusively at the terminal vinyl carbon.
•
+
•+
The divergent regiochemistry of 1 and 8 (even though the tethers between vinylcyclopropane
and alcohol functions differ only by a single CH
course of nucleophilic capture in radical cations.
2
group) elucidates the principles governing the
In tr od u ction
Vinylcyclopropane radical cation, the simplest species
containing an olefinic moiety and a cyclopropane ring,
Radical cations of molecules containing strained ring
7-11
has only recently been characterized adequately.
The
moieties as well as olefinic fragments have been the focus
molecular ion of vinylcyclopropane rearranges to penta-
1
of much interest in recent years, including the conjuga-
8
1
,3-diene radical cation in the gas phase. Related rear-
tive and homoconjugative interactions between the two
types of functions. Various substrates have been probed
to delineate changes in the molecular geometry upon one-
electron oxidation and to assess the spin and charge
density distributions in the resulting radical cations.2
Typically, the reactions of strained ring radical cations
proceed with release of ring strain;3,4 in some systems,
this reaction is assisted by a nucleophile.5
rangements of two rigidly linked vinylcyclopropane sys-
tems in solution (sabinene to â-phellandrene; R-thujene
to R-phellandrene) were interpreted as novel radical
9
cation sigmatropic shifts. The unsubstituted prototype
reacted with nucleophiles by preferential (though not
exclusive) capture at the cyclopropane ring.10 In contrast,
the cis-chrysanthemol radical cation, bearing an internal
nucleophile, failed to react by capture of the quaternary
cyclopropane carbon; instead, it underwent regiospecific
intramolecular capture at the terminal carbon of the vinyl
group.11
-7
(1) (a) Forrester, R. A.; Ishizu, K.; Kothe, G.; Nelsen, S. F.; Ohya-
Nishiguchi, H.; Watanabe, K.; Wilker, W. Organic Cation Radicals and
Polyradicals. In Landolt-B o¨ rnstein, Numerical Data and Functional
Relationships in Science and Technology; Springer-Verlag: Heidelberg,
In this publication, we describe the intramolecular
•
+
1
980; Volume IX, Part d2. (b) Shida, T. Electronic Absorption Spectra
capture of a vinylcyclopropane radical cation, 1 , in
which the internal nucleophile is attached by an extended
tether containing an additional methylene group. The
of Radical Ions; Elsevier: Amsterdam, 1988. (c) Shida, T.; Haselbach,
E.; Bally, T. Acc. Chem. Res. 1984, 17, 180. (d) Nelsen, S. F. Acc. Chem.
Res. 1987, 20, 269. (e) Roth, H. D. Top. Curr. Chem. 1992, 163, 133-
•
+
2
45.
(
intramolecular capture of 1 features the competition
2) (a) Haddon, R. C.; Roth, H. D. Croat. Chem. Acta 1984, 57, 1165.
b) Roth, H. D.; Schilling, M. L. M. Can. J . Chem. 1983, 61, 1027. (c)
Roth, H. D.; Schilling, M. L. M.; Schilling, F. C. J . Am. Chem. Soc.
985, 107, 4152. (d) Roth, H. D.; Schilling, M. L. M.; Abelt, C. J .
•+
between a five-membered transition state (1 -5-TS) for
(
attack at the cyclopropane carbon in S
N
2 fashion and a
seven-membered one (1 -7-TS) for attack at the terminal
vinyl carbon, respectively, in S 2′ fashion.
•+
1
Tetrahedron 1986, 42, 6157. (e) Roth, H. D.; Schilling, M. L. M.; Abelt,
C. J . J . Am. Chem. Soc., 1986, 108, 6098. (f) Roth, H. D. Acc. Chem.
Res. 1987, 20, 343-350. (g) Roth, H. D.; Du, X.-M.; Weng, H.;
Lakkaraju, P. S.; Abelt, C. J . J . Am. Chem. Soc., 1994, 116, 7744-
N
7
1
752. (h) Weng, H.; Du, X.-M.; Roth, H. D. J . Am. Chem. Soc. 1995,
17, 135-140.
(
3) Quadricyclane to norbornadiene rearrangement: (a) Roth, H. D.;
Schilling, M. L. M.; J ones, G., II. J . Am. Chem. Soc. 1981, 103, 1246-
1
7
248. (b) Roth, H. D.; Schilling, M. L. M. J . Am. Chem. Soc. 1981, 103,
210-7217.
(
4) Methylenecyclopropane cycloaddition: (a) Takahashi, Y.; Mukai,
T.; Miyashi, T. J . Am. Chem. Soc. 1983, 105, 6511-6513. (b) Miyashi,
T.; Takahashi, Y.; Mukai, T.; Roth, H. D.; Schilling, M. L. M. J . Am.
Chem. Soc. 1985, 107, 1079-1080.
(6) Bicyclobutane systems: (a) Gassman, P. G.; Olson, K. D.; Walter,
L.; Yamaguchi, R. J . Am. Chem. Soc. 1981, 103, 4977. (b) Gassman,
P. G.; Olson, K. D. J . Am. Chem. Soc. 1982, 104, 3740.
(7) Vinylcyclopropane systems: (a) Weng, H.; Sethuraman, V.; Roth,
H. D. J . Am. Chem. Soc. 1994, 116, 7021-7025. (b) Arnold, D. R.; Du,
X.; de Lijser, H. J . P. Can. J . Chem. 1995, 73, 522-530.
(8) Dass, C.; Peake, D. A.; Gross, M. L. Org. Mass. Spectrom. 1986,
21, 741-746.
(
5) Cyclopropane systems: (a) Rao, V. R.; Hixson, S. S. J . Am. Chem.
Soc. 1979, 101, 6458-6459. (b) Mizuno, K.; Ogawa, J .; Kagano, H.;
Otsuji, Y. Chem. Lett. 1981, 437-438. (c) Mizuno, K.; Ogawa, J .; Otsuji,
Y. Chem. Lett. 1981, 741-744. (d) Mazzocchi, P. H.; Somich, C.;
Edwards, M.; Morgan, T. Ammon, H. L. J . Am. Chem. Soc. 1986, 108,
6
828. (e) Dinnocenzo, J . P.; Todd, W. P.; Simpson, T. R.; Gould, I. R.
J . Am. Chem. Soc. 1990, 112, 2462-2464. (f) Hixson, S. S.; Xing, Y.
Tetrahedron Lett. 1991, 32, 173-174. (g) Dinnocenzo, J . P.; Lieberman,
D. R.; Simpson, T. R. J . Am. Chem. Soc. 1993, 115, 366-367.
(9) Weng, H.; Sheik, Q.; Roth, H. D. J . Am. Chem. Soc. 1995, 117,
10655-10661.
1
0.1021/jo9903048 CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/29/1999