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The nicotinic acetylcholine receptor (nAChR) is one of the targets for developing drugs for the treatment of central nervous system (CNS) disorders and for control of agricultural pests. Pyrido[3,4‐b] homotropane (PHT) was originally designed and synthesized by Kanne and co‐workers and showed strong affinity binding to nAChR. PHT has a novel aza‐[4.2.1]nonane skeleton. Owing to its excellent biological activities and novel chemical structure, synthetic and medicinal chemists have been attracted by this molecule. Some PHT analogues with bridged aza‐[n.2.1] skeletons were also designed and synthesized via different strategies. Herein, we summarize the syntheses of PHT and its analogues. Their biological activity study is also briefly discussed. [ABSTRACT FROM AUTHOR]

Abstract: An efficient synthesis of (−)‐pyrido[3,4‐b]homotropane (PHT) as well as (±)‐PHT has been achieved in 7 steps from conveniently available starting materials. Key transformations involve an efficient construction of the core bridged 9‐aza‐[4.2.1]nonane skeleton via a Sc(OTf)3‐catalyzed intramolecular cross [3+2] cycloaddition (IMCC) followed by Krapcho decarboxylation and Barton reductive decarboxylation. The present work supplies a general and efficient strategy for synthesis of other bridged analogues. [ABSTRACT FROM AUTHOR]

A novel Lewis acid-catalyzed [3+2] intramolecular cross-cycloaddition (IMCC) between aziridine 2,2-diesters and conjugated dienes has been developed. This is the first regiospecific IMCC of intramolecular 1,3-dipolar cycloadditions of azomethine ylides with carbon=carbon double bonds, and supplies a general and efficient strategy for construction of structurally complex and diverse aza-[ n.2.1] skeletons. The [3+2]IMCC could be carried out under mild conditions and in gram scale. More importantly, 3-alkyl-substituted aziridines were also successful. The excellent structural diversity, the facile operation and the versatile post-modifications will support the applications of the [3+2]IMCC in natural products synthesis and drugs discovery. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In contast to the general [4+2] cycloaddition reactions of alkynylcyclopropane ketones reported in the literature, we report herein a Sc(OTf)3-catalyzed formal intermolecular [3+2] cycloaddition reaction of alkynylcyclopropane ketones with electron-rich aromatic aldehydes. 2,3,3,5-Tetrasubstituted tetrahydrofurans were obtained by this method, and the tetrahydrofuran skeleton was diastereoselectively constructed with a 2,5- trans configuration. This is also quite different to the 2,5- cis configuration usually obtained from typical [3+2] cycloaddition reactions of most donor-acceptor cyclopropanes. Additionally, the cycloadducts were subjected to a domino carbopalladation/C-H activation/C-C bond-formation process for the highly efficient construction of polycyclic skeletons. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Carbon bridges: The title reaction has been successfully developed, and applied to the total synthesis of the tetracyclic diterpenoids phyllocladanol and phyllocladene. The method provides an efficient, general, and conceptually new strategy for the construction of structurally complex and diverse [n.2.1] carbocyclic skeletons (see scheme). [ABSTRACT FROM AUTHOR]

A novel Lewis acid‐catalyzed [3+2] intramolecular cross‐cycloaddition (IMCC) between aziridine 2,2‐diesters and conjugated dienes has been developed, which supplies a general and efficient strategy for construction of structurally complex and diverse aza‐[n.2.1] skeletons. The excellent structural diversity, the facile operation and the versatile post‐modifications will support the applications of the [3+2]IMCC in natural product synthesis and drug discovery. “Three begets all things of the world” comes from “Daodejing”, an immortal classic composed by Laozi, a great philosopher and thinker of ancient China. In this chemistry, the three‐membered aziridine means the “three” which begets the diversity and complexity by the IMCC strategy. For the full story see the Communication by Z. Wang et al. on page 17862 ff. [ABSTRACT FROM AUTHOR]

Cycloadditions Developing efficient and general strategies for construction of skeletally complex and diverse polycyclic skeletons in natural products is important and challenging in organic synthesis. In their Communication on page 1231 ff., Z. Wang and co‐workers demonstrate a [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, bridged trans‐[5.3.0]decane skeleton and its corresponding structurally complex and diverse polycyclic ones are constructed efficiently. This strategy is believed to be of potential importance to natural product synthesis and drug discovery. [ABSTRACT FROM AUTHOR]

Abstract: A highly regioselective tandem 1,3-dipolar cycloaddition of cyclopropene 1,1-diesters with nitrile oxides was described. This reaction supplied a new method for synthesis of polyfunctionalized isoxazole derivatives in moderate to excellent yields under mild conditions. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: 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. [ABSTRACT FROM AUTHOR]