Rh(I)-catalyzed benzo/[7+1] cycloaddition of cyclopropyl-benzocyclobutenes and CO by merging thermal and metal-catalyzed C-C bond cleavages.

A Rh-catalyzed benzo/[7+1] cycloaddition of cyclopropyl-benzocyclobutenes (CP-BCBs) and CO to benzocyclooctenones has been developed. In this reaction, CP-BCB acts as a benzo/7-C synthon and the reaction involves two C-C bond cleavages: a thermal electrocyclic ring-opening of the four-membered ring in CP-BCB and a Rh-catalyzed C-C cleavage of the cyclopropane ring.

Transition metal-catalyzed cycloadditions of cyclopropanes for the synthesis of carbocycles: C-C activation in cyclopropanes.

Transition metal-catalyzed cycloadditions of cyclopropanes have been well developed over the past several decades, leading to numerous new types of cycloadditions which are complementary to the traditional cycloadditions for the synthesis of carbocycles. Cycloadditions of vinylcyclopropanes (VCPs) and methylenecyclopropanes (MCPs) constitute two main aspects of this field. VCPs can act either as five-carbon synthons or three-carbon synthons, depending on whether the vinyl substituent is acting as an additional two-carbon synthon or not. As five-carbon synthons, VCPs are involved in [5+1], [5+2], [5+2+1], and [5+1+2+1] cycloadditions. As three-carbon synthons, VCPs are mainly involved in [3+2] and [3+2+1] cycloadditions. MCPs mostly act as three-carbon synthons and can have [3+2] cycloadditions with different π systems. Other types of cycloadditions involving MCPs are also reviewed, such as [3+1], [3+2+2], and [4+3+2] cycloadditions. Cycloadditions of some other unusual cyclopropane derivatives are also introduced briefly. The cycloadditions of VCPs and MCPs have found applications in total synthesis and some representative molecules are tabulated as selected examples.

Rh(I)-catalyzed [5+1] cycloaddition of vinylcyclopropanes and CO for the synthesis of α,ß- and ß,γ-cyclohexenones.

A cationic Rh(I)-catalyzed [5 + 1] cycloaddition of vinylcyclopropanes and CO has been developed, affording either ß,γ-cyclohexenones as major products or α,ß-cyclohexenones exclusively, under different reaction conditions.

Total synthesis of (+)-asteriscanolide: further exploration of the rhodium(I)-catalyzed [(5+2)+1] reaction of ene-vinylcyclopropanes and CO.

The total synthesis of (+)-asteriscanolide is reported. The synthetic route features two key reactions: 1) the rhodium(I)-catalyzed [(5+2)+1] cycloaddition of a chiral ene-vinylcyclopropane (ene-VCP) substrate to construct the [6.3.0] carbocyclic core with excellent asymmetric induction, and 2) an alkoxycarbonyl-radical cyclization that builds the bridging butyrolactone ring with high efficiency. Other features of this synthetic route include the catalytic asymmetric alkynylation of an aldehyde to synthesize the chiral ene-VCP substrate, a highly regioselective conversion of the [(5+2)+1] cycloadduct into its enol triflate, and the inversion of the inside-outside tricycle to the outside-outside structure by an ester-reduction/elimination to enol-ether/hydrogenation procedure. In addition, density functional theory (DFT) rationalization of the chiral induction of the [(5+2)+1] reaction and the diastereoselectivity of the radical annulation has been presented. Equally important is that we have also developed other routes to synthesize asteriscanolide using the rhodium(I)-catalyzed [(5+2)+1] cycloaddition as the key step. Even though these routes failed to achieve the total synthesis, these experiments gave further useful information about the scope of the [(5+2)+1] reaction and paved the way for its future application in synthesis.