Annulation

About: Annulation is a research topic. Over the lifetime, 10152 publications have been published within this topic receiving 189701 citations.

Rapid Access to Polyprenylated Phloroglucinols via Alkylative Dearomatization−Annulation: Total Synthesis of (±)-Clusianone1

Abstract: A concise approach to the bicyclo[3.3.1]nonane framework of the polyprenylated phloroglucinol natural products utilizing a tandem alkylative dearomatization−annulation sequence is described. Syntheses of (±)-clusianone and a complex adamantane framework have been achieved using the developed methodology.

An Unexpected Phosphine-Catalyzed Regio- and Diastereoselective [4+1] Annulation Reaction of Modified Allylic Compounds with Activated Enones

Abstract: Nucleophilic phosphines are known to be useful mild catalysts for the synthesis of cyclic and heterocyclic compounds. Generally, tertiary-phosphine-mediated annulations are triggered by nucleophilic addition of phosphines to activated compounds. The resultant zwitterionic intermediates can react with various electrophiles such as aldehydes, imines, and activated polarized C=C bonds to furnish cyclic compounds. Herein, we report a phosphine-catalyzed highly diastereoselective synthesis of tetrasubstituted 2,3-dihydrofurans, which are subunits of a range of biologically active compounds (e.g., aflatoxin B1 and clerodin), [4] via [4+1] annulations of Morita–Baylis–Hillman carbonates with activated enones. In these annulations, Morita–Baylis– Hillman carbonates act as the one-carbon unit, which is distinguished from the modified allylic compounds reported by Lu et al. as the three-carbon units, such as in [3+2], [3+3], [3+4], and [3+6] annulation reactions. In recent years, Morita–Baylis–Hillman adducts have been illustrated as suitable starting materials for the synthesis of a variety of multifunctional compounds. During our study of the new chemistry of electron-deficient enynes, we became interested in the annulation between Morita– Baylis–Hillman carbonate 1a and conjugated yne-enone 2a. We were pleased to find that the reaction proceeded smoothly in toluene at room temperature under catalysis with 10 mol% PPh3, leading to a [4+1] adduct, 2,3-dihydrofuran 3a, in 72% yield of isolated product with 20:1 diastereoselectivity (Table 1, entry 1). The structure of 3a was established by X-ray crystallography analysis of the analogous product 3f (R=p-BrC6H4; Figure 1). [7] To improve the yield of 3a, various solvents and tertiary phosphines were tested and the results are summarized in Table 1. A higher product yield was obtained when the reaction was performed in CH2Cl2, while the selectivity was slightly decreased (Table 1, entry 2). Good yields with high selectivity were also obtained in DCE, Et2O, and 1,4-dioxane, albeit the reactions require a longer time to go to completion (Table 1, en-

Catalytic enantioselective alkylative dearomatization-annulation: total synthesis and absolute configuration assignment of hyperibone K.

Abstract: The asymmetric total synthesis of the polyprenylated acylphloroglucinol hyperibone K has been achieved using an enantioselective alkylative dearomatization−annulation process. NMR and computational studies were employed to probe the mode of action of a chiral phase-transfer (ion pair) catalyst.

p‐tert‐Butylcalix[4]arene

Abstract: p-tert-Butylcalix[4]arene reactant: p-tert-Butylphenol from Aldrich Chemical Company, Inc. product: p-tert-butylcalix[4]arene Keywords: annulation, carbocyclic-[>6]; cyclization, condensation

Palladium‐Mediated Annulation of Vinyl Aziridines with Michael Acceptors: Stereocontrolled Synthesis of Substituted Pyrrolidines and Its Application in a Formal Synthesis of (−)‐α‐Kainic Acid

Abstract: route to vinyl epoxides and vinyl aziridines via chiral sulfur ylides, we were keen to develop their potential in synthesis further. It had been reported that palladium-catalyzed reactions of vinyl epoxides and aziridines with doubly activated Michael acceptors gave tetrahydrofurans and pyrrolidines in good yield but usually with poor stereocontrol. However, related reactions with singly activated Michael acceptors were not effective. Nevertheless, we recognized that if we could find a way of coercing vinyl aziridines to react with singly activated enones/acrylates, and we were able to control stereochemistry in the annulation process, then we could potentially utilize this methodology in synthesis. Herein, we describe our success in simultaneously meeting these two significant challenges and also describe its application in a formal synthesis of ( )-a-kainic acid 1. Our initial efforts at promoting reaction between vinyl aziridine 2a and methyl vinyl ketone (MVK, A) using [Pd2(dba)3·CHCl3], (p-FC6H5)3P in THF (conditions employed by Yamamoto), however, were fruitless—we only observed decomposition. Using trimethylsilyl-substituted trans vinyl aziridine 2e, we now observed isomerization to a mixture of trans/cis aziridines (1:20). With this substrate, clearly the Pd was performing its role in generating the p-allyl palladium complex as this resulted in isomerization of the vinyl aziridine. However, the amide anion that was generated did not react with the enone. This result reinforced the observations by Yamamoto and Knight that doubly activated Michael acceptors were required to capture the relatively unreactive amide anion. We reasoned that ion pairing of the amide anion with the cationic Pd complex might compromise its reactivity, and that increased nucleophilicity should therefore be possible with an anionic Pd complex instead (Scheme 2).