Tetrakis[N-[4-dodecylphenyl)sulfonyl]-(S)-prolinate]dirhodium [Rh(2)(S-DOSP)(4)]-catalyzed decomposition of methyl aryldiazoacetates in the presence of substituted ethylbenzenes results in benzylic C-H activation by means of a rhodium-carbenoid-induced C-H insertion. A Hammet study showed that positive charge buildup occurred on the benzylic carbon in the transition state of the C-H activation step. C-H activation of toluene and isopropylbenzene is possible, but a competing double cyclopropanation occurs with these substrates. The C-H activation is highly regioselective and enantioselective, and in certain cases, moderate diastereoselectivity is also possible.

The C-H activation of silyl ethers by means of rhodium carbenoid-induced C-H insertion represents a very direct method for the stereoselective synthesis of silyl-protected beta-hydroxy esters. The reaction can proceed with very high regio-, diastereo-, and enantioselectivity and represents a surrogate to the aldol reaction. The reaction is catalyzed by the rhodium prolinate complex Rh(2)(S-DOSP)(4). A critical requirement for the high chemoselectivity is the use of donor/acceptor-substituted carbenoids such as those derived from methyl aryldiazoacetates. A range of silyl ethers may be used such as allyl silyl ethers, tetraalkoxysilanes, and even simple trimethylsilyl alkyl ethers. In general, C-H activation preferentially occurs at methylene sites, as the reactivity is controlled by a delicate balance between steric and electronic effects.

[reaction: see text]. Tetrakis[N-[4-dodecylphenyl)sulfonyl]-(S)-prolinato]-dirhodium [Rh2(S-DOSP)4] catalyzed decomposition of methyl aryldiazoacetates in the presence of alkenes results in allylic C-H activation by means of a rhodium-carbene induced C-H insertion. The resulting gamma,delta-unsaturated esters are equivalent to products that would be traditionally obtained from an asymmetric Claisen rearrangement. Highly regio- and enantioselective C-H insertions can be achieved, and in certain cases, good diastereocontrol is also possible.

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The Rh2(S-DOSP)4-catalyzed reaction of vinyldiazoacetates with dihydronaphthalenes results in a highly enantioselective (91-99.6% ee) and diastereoselective (>98% de) C-H functionalization. The apparent intermolecular C-H insertion was demonstrated to be a combined C-H activation/Cope rearrangement followed by a retro-Cope rearrangement.