SCHEME 1. Novel Ambiphilic Dichlorocarbenoid in Alkene
Cyclopropanation and Carbonyl Olefination
Novel Ambiphilic Dichlorocarbenoid Equivalent
in Alkene Cyclopropanation and Carbonyl
Olefination
Ching-Ting Chien, Chia-Chung Tsai, Chi-Hui Tsai,
Tsai-Yuan Chang, Ping-Kuei Tsai, Ying-Chuan Wang, and
Tu-Hsin Yan*
Department of Chemistry, National Chung-Hsing UniVersity,
Taichung 400, Taiwan, Republic of China
SCHEME 2. Optimized Conditions for the
TiCl4-Mg-Promoted Dichlorocarbene Transfer of CCl4
ReceiVed December 20, 2005
The Ti-Mg-dichloromethylene complexes derived from the
oxidative addition of CCl4 to the Mg-TiCl4 bimetallic
species serve as a novel class of ambiphilic dichlorocarbenoid
equivalents. Not only is Ti-Mg-dichlorocarbenoid highly
selective but also it seems highly reactive in both alkene
cyclopropanations and carbonyl dichloromethylenations.
flexibility. Extensive interest in titanium-carbenoid-mediated
reactions led us to record the first examples of the Ti-Mg-
dichloromethylene complex participating as an ambiphilic
dichlorocarbenoid, which not only efficiently effected highly
selective cyclopropanation of alkenes but also displayed highly
nucleophilic reactivity, leading to the dichloromethylenation of
readily enolizable or sterically hindered carbonyls.
Dichlorocarbenoids exhibit reactivity ranging from electro-
philic to nucleophilic. All reported examples of dichlorocar-
benoid-mediated coupling reactions record it as participating
as either a nucleophile1 in carbonyl olefinations or an electro-
phile2 in olefin cyclopropanations. For there to be no discon-
tinuity between electrophilic and nucleophilic behavior, there
must exist ambiphilic dichlorocarbenoids, which act as a Fischer-
type complex3 toward alkenes and as a Schrock-type complex4
toward carbonyl compounds (Scheme 1). Changing the reaction
profile whereby the same readily available carbenoid can be
channeled into a different adduct greatly expands synthetic
For the alkene cyclopropanation, we examined the use of the
Ti-Mg bimetallic species5,6 to promote dichlorocarbene transfer
of CCl4. Adding the simple cyclohexene 1 to CCl4 (10 equiv),
TiCl4 (1 equiv), and Mg (4 equiv) in 1,2-dichloroethane followed
by THF at 0 °C did indeed complete cyclopropanation within
0.5 h, leading to the desired dichlorocyclopropane 1a (Scheme
2, method A).
Remarkably, even a catalytic amount of TiCl4 sufficed to
completely effect cyclopropanation of 1a albeit in a slower
reaction. Thus, after 1∼2 h, using 5-10 mol % of TiCl4 and
stoichiometric quantities of CCl4 and Mg gave a 95% yield of
adduct 1a. Cyclopentene 2 gave similar results under our
standard conditions. Cyclopropanation onto styrene 3 also led
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10.1021/jo052610t CCC: $33.50 © 2006 American Chemical Society
Published on Web 05/05/2006
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J. Org. Chem. 2006, 71, 4324-4327