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A novel tandem reaction by combination of Diels–Alder [4+2] cycloaddition and [3+2] IMCC (intramolecular cross-cyclo­addition) of dienylcyclopropane 1,1-diesters has been successfully developed. In this reaction, three new rings and four new stereocenters were generated in one-pot. This supplies a strategy for rapid construction of 6,6- and 6,7-fused carbocyclic skeletons which are common cores in many biologically important natural products.

An acid-catalyzed domino Meinwald rearrangement of epoxides/intramolecular [3+2] cross-cycloaddition of cyclopropane 1,1-diesters was developed. This supplied a method for the construction of bridged oxa-[n.2.1] (n = 3, 4) skeletons.

Aiming to develop efficient and general strategies for construction of complex and diverse polycyclic skeletons, we have successfully developed [4+3]IMPC (intramolecular parallel cycloaddition) of cyclopropane 1,1-diesters with [3]dendralenes. With a combination of the [4+3]IMPC and subsequent [4+n] cycloadditions, trans-[5.3.0]decane skeleton and its corresponding structurally complex and diverse polycyclic variants could be constructed efficiently. This novel [4+3] cycloaddition reaction mode of donor–acceptor cyclopropanes proceeds as a result of the ring-strain relief of a trans-[3.3.0]octane. We strongly believe that the developed methods will demonstrate potential applications in natural products synthesis and drug discovery.

A triflic acid-catalyzed formal [3 + 2] cycloaddition of cyclopropane 1,1-diesters with nitriles was developed. This reaction was expeditious, and the scope of the substituents in both cyclopropanes and nitriles was broad. This supplies an efficient and practical method for the synthesis of 1-pyrrolines.

A novel Lewis acid promoted formal intramolecular [3 + 2] parallel/cross-cycloaddition of cyclopropane 1,1-diesters with allenes has been successfully developed, in which the two C═C of allenes were involved respectively. This provides a general and efficient strategy for the construction of structurally diverse [4.3.0]nonane and [3.2.1]octane skeletons.

The title reaction is successfully developed, and applied to the total synthesis of the tetracyclic diterpenoids phyllocladanol (XX) and phyllocladene (XXI).

A novel Lewis acid catalyzed formal intramolecular [3 + 3] cross-cycloaddition (IMCC) of cyclopropane 1,1-diesters has been successfully developed. This supplies an efficient and conceptually new strategy for construction of bridged bicyclo[2.2.2]octane skeletons. This [3 + 3]IMCC could be run up to gram scale and from easily prepared starting materials. This [3 + 3]IMCC, together with our previously reported [3 + 2]IMCC strategy, can afford either the bicyclo[2.2.2]octane or bicyclo[3.2.1]octane skeletons from the similar starting materials by regulating the substituents on vinyl group.

In this account we have systematically described the acid-promoted intramolecular cycloadditions of activated cyclo­propanes, which were conceptually classified into intramolecular cross-cycloadditions (IMCC) and intramolecular parallel-cyclo­additions. The IMCC provided a general and efficient strategy for construction of structurally complex and diverse bridged bicyclic skeletons. The potential of this strategy has been demonstrated by the synthesis of natural products. 1 Introduction 2 [3+2]IMCC of Cyclopropane 1,1-Diester with C=O 3 [3+2]IMCC of Cyclopropane 1,1-Diester with C=N 4 [3+2]IMCC of Cyclopropane 1,1-Diester with C=C 5 [3+3]IMCC of Cyclopropane 1,1-Diester with Nitrones 6 [3+2]IMCC of Mono-donor/Mono-acceptor Cyclopropane with C=O 7 Lewis Acid Regulated Domino Cycloisomerization/[4+2]IMCC or [3+2]IMCC of Alkynylcyclopropane Ketone with C=O and C=N 8 Conclusions and Outlook

A novel tandem reaction of vinylcyclopropane ketone with benzaldehyde has been successfully developed. This provides a new method for the preparation of γ-oxo-hexenone derivatives from easily accessible starting materials.

Total synthesis of natural product (±)-bruguierol A was accomplished in 10-steps and with an overall 16.8% yield. The embedded unique 8-oxabicyclo[3.2.1]octane core skeleton in this natural product was constructed via a novel Sc(OTf) 3 -catalyzed intramolecular [3+2] cycloaddition of cyclopropane, which was developed recently in this laboratory. This general synthetic strategy can be potentially applied to the synthesis of a broad range of structurally related natural products.

A Lewis acid promoted intramolecular [3+2] cycloaddition of cyclopropane 1,1-diesters with aldehydes, ketones, and imines is developed to provide a general and efficient strategy for construction of bridged oxa- and aza-[n.2.1] skeletons.

We report herein an nBuLi-mediated, expeditious, ring-opening rearrangement of (arylmethylene)cyclopropane 1,1-diesters to prepare 1,3-diene derivatives with good stereoselectivity. The reaction mechanism has also been discussed.

Catalyzed by Lewis acids, donor–acceptor cyclopropane 1,1-diesters reacted with enol silyl ethers to afford 1,6-dicarbonyl compounds in moderate to excellent yields. This supplied a mild carbon–carbon bond-forming method from the ring opening of cyclopropanes. A smooth tandem [3+2] cycloaddition/ring opening process has been clearly proved by an independent experiment.

An activated vinyl cyclopropane reacted with substituted benzaldehydes to afford α-methylene γ-butyrolactones in the presence of DABCO·6H2O. This tandem domino process took place in aqueous media, and was presumably initiated with the ring opening of cyclopropane by the nucleophilic addition of DABCO·6H2O.

A novel Lewis acid catalyzed formal intramolecular [3 + 3] cross-cycloaddition (IMCC) of cyclopropane 1,1-diesters has been successfully developed. This supplies an efficient and conceptually new strategy for construction of bridged bicyclo[2.2.2]octane skeletons. This [3 + 3]IMCC could be run up to gram scale and from easily prepared starting materials. This [3 + 3]IMCC, together with our previously reported [3 + 2]IMCC strategy, can afford either the bicyclo[2.2.2]octane or bicyclo[3.2.1]octane skeletons from the similar starting materials by regulating the substituents on vinyl group.

A tandem isomerization/intramolecular [3 + 2] cross-cycloaddition (IMCC) of cyclopropane 1,1-diesters with α,β-unsaturated ketones/aldehydes under a cooperative catalysis of photo and Lewis acids has been successfully developed. This supplied a general and efficient strategy for construction of medium-sized carbocyclic (8-, 9-, and 10-membered) skeletons as well as such carbocycle-based bridged oxa-bicyclo[n.2.1] (n = 4-6) skeletons.

An acid-catalyzed domino Meinwald rearrangement of epoxides/intramolecular [3+2] cross-cycloaddition of cyclopropane 1,1-diesters was developed. This supplied a method for the construction of bridged oxa-[n.2.1] (n = 3, 4) skeletons.

A triflic acid-catalyzed formal [3 + 2] cycloaddition of cyclopropane 1,1-diesters with nitriles was developed. This reaction was expeditious, and the scope of the substituents in both cyclopropanes and nitriles was broad. This supplies an efficient and practical method for the synthesis of 1-pyrrolines.

A novel Lewis acid promoted formal intramolecular [3 + 2] parallel/cross-cycloaddition of cyclopropane 1,1-diesters with allenes has been successfully developed, in which the two C═C of allenes were involved respectively. This provides a general and efficient strategy for the construction of structurally diverse [4.3.0]nonane and [3.2.1]octane skeletons.

The title reaction is successfully developed, and applied to the total synthesis of the tetracyclic diterpenoids phyllocladanol (XX) and phyllocladene (XXI).

In this account we have systematically described the acid-promoted intramolecular cycloadditions of activated cyclo­propanes, which were conceptually classified into intramolecular cross-cycloadditions (IMCC) and intramolecular parallel-cyclo­additions. The IMCC provided a general and efficient strategy for construction of structurally complex and diverse bridged bicyclic skeletons. The potential of this strategy has been demonstrated by the synthesis of natural products. 1 Introduction 2 [3+2]IMCC of Cyclopropane 1,1-Diester with C=O 3 [3+2]IMCC of Cyclopropane 1,1-Diester with C=N 4 [3+2]IMCC of Cyclopropane 1,1-Diester with C=C 5 [3+3]IMCC of Cyclopropane 1,1-Diester with Nitrones 6 [3+2]IMCC of Mono-donor/Mono-acceptor Cyclopropane with C=O 7 Lewis Acid Regulated Domino Cycloisomerization/[4+2]IMCC or [3+2]IMCC of Alkynylcyclopropane Ketone with C=O and C=N 8 Conclusions and Outlook

Build a bridge: The first catalytic intramolecular [3+2] cycloaddition of monodonor-monoacceptor cyclopropanes (see scheme) provides a general and efficient strategy for construction of structurally diverse acetal[n.2.1] and 1,4-dioxygen-substituted cyclic skeletons, which are widely distributed in biologically important natural products.

A Lewis acid promoted intramolecular [3+2] cycloaddition of cyclopropane 1,1-diesters with aldehydes, ketones, and imines is developed to provide a general and efficient strategy for construction of bridged oxa- and aza-[n.2.1] skeletons.

We report herein an nBuLi-mediated, expeditious, ring-opening rearrangement of (arylmethylene)cyclopropane 1,1-diesters to prepare 1,3-diene derivatives with good stereoselectivity. The reaction mechanism has also been discussed.

Catalyzed by Lewis acids, donor–acceptor cyclopropane 1,1-diesters reacted with enol silyl ethers to afford 1,6-dicarbonyl compounds in moderate to excellent yields. This supplied a mild carbon–carbon bond-forming method from the ring opening of cyclopropanes. A smooth tandem [3+2] cycloaddition/ring opening process has been clearly proved by an independent experiment.

An activated vinyl cyclopropane reacted with substituted benzaldehydes to afford α-methylene γ-butyrolactones in the presence of DABCO·6H2O. This tandem domino process took place in aqueous media, and was presumably initiated with the ring opening of cyclopropane by the nucleophilic addition of DABCO·6H2O.