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We describe a method for the synthesis of various 2‐silyloxy‐2‐norbornen‐7‐ones by exploiting the specific reactivity of the 1,4‐bis(silyloxy)‐1,3‐cyclopentadiene framework, which is generated by the silylation of a 2,2‐disubstituted‐1,3‐cyclopentanedione bearing a picolinoyloxy group at the 2′ position of its C‐2 side chain. The release of the acyloxy group during the reaction generates carbocations that are then attacked by silyloxy‐substituted carbons in the 1,4‐bis(silyloxy)‐1,3‐cyclopentadiene moiety skeleton, forming a 4,5‐cis‐fused ring skeleton. Skeletal rearrangement of the bicyclic core results in the formation of the corresponding 2‐silyloxy‐2‐norbornen‐7‐one. This novel transformation of 1,3‐cyclopentanedione moieties can be used to synthesise other cyclopentenone‐fused bicyclic frameworks. [ABSTRACT FROM AUTHOR]

2,2-Disubstituted 1,3-cyclopentanediones are versatile building blocks for synthesizing complex natural products with bicyclic structures including cyclopentane rings. The reported method for the synthesis of these compounds involves the semi-pinacol rearrangement of a Mukaiyama aldol adduct prepared from a ketone/ketal and 1,2-bis(trimethylsilyloxy)cyclobutene. However, the adoption of α-oxy-functionalized ketones/ketals is quite difficult, as demonstrated by our experiments. To overcome this limitation of the method, 2-acylfuran derivatives were used as the reactants to synthesize 2,2-disubstituted 1,3-cyclopentanediones. Furthermore, two reaction conditions, that is, the use of 1.4 equivalents of a boron trifluoride-diethyl ether complex or 0.4 and 0.2 equivalent of trimethylsilyl triflate and methoxytrimethylsilane, respectively, were established for the conversion of 2-acylfurans into the corresponding 1,3-cyclopentanediones in acceptable yields. The transformations of the furan rings in the obtained products were also investigated. [ABSTRACT FROM AUTHOR]

Ent‐kaurenes consist of an ABC‐ring based on a trans‐anti‐hydrophenanthrene skeleton and a D ring with an exomethylene. Highly oxygen‐functionalized ent‐kauren‐15‐ones have promising antiinflammatory pharmacological activity. In this study, we developed a novel diastereoselective synthesis of trans‐anti‐hydrophenanthrenes via a Ti‐mediated reductive radical cyclization. We also demonstrated the applicability of this method by developing the first total synthesis of (±)‐kamebanin (longest linear sequence; 17 steps, overall yield; 6.5 %). Furthermore, this synthesis provided a formal semi‐pinacol rearrangement for the construction of the quaternary carbon at C8 and a novel Thorpe‐Ziegler‐type reaction for the construction of the D‐ring. [ABSTRACT FROM AUTHOR]

The article titled "Unique Reactivity of the 1,4-Bis(silyloxy)-1,3-cyclopentadiene Moiety: Application to the Synthesis of 7-Norbornanone Derivatives" explores a novel reaction system that allows the carbonyl carbon in the 1,3-cyclopentadione motif to behave as a nucleophile, despite carbonyl carbons typically lacking nucleophilicity. This technique enables the formation of a cyclization to create a cyclobutane ring, which can then be transformed into a 7-norbornanone derivative through skeletal rearrangement. The research article provides more detailed information on this topic. [Extracted from the article]

Synthetic studies on an ABC-ring model of tubiferal A, a triterpenoid isolated from the fruit bodies of the Tubifera dimorphotheca myxomycete, are described. The stereogenic centers at the angular positions were constructed through the stereoselective addition of a C-ring allylborane followed by an Eschenmoser–Claisen rearrangement reaction prior to the formation of the AB-ring system by a double intramolecular alkylation reaction of a dichloro nitrile intermediate. [ABSTRACT FROM AUTHOR]

Daphniphyllum alkaloids have complex molecular structures; consequently, their synthesis can be challenging. A new method for the construction of the [7-5-5] tricyclic core of Daphniphyllum alkaloids was developed. The bicyclo[5.3.0]decane skeleton was constructed through a divinylcyclopropane rearrangement of a cyclopentenone derivative with a vinylcyclopropyl group at the β-position. After introduction of a 2-iodoethyl group by a regioselective Michael addition with phenyl vinyl selenone, the [7-5-5] tricyclic system was formed by intramolecular alkylation of a cyclopentadienyl anion species. [ABSTRACT FROM AUTHOR]

Generally, glycosylation reactions activate an anomeric substituent in a glycosyl donor to generate an oxocarbenium ion intermediate. Here we report a novel glycosylation reaction triggered by the activation of a 2-O-substituted propargyl group in a 3,6- O -1,1′-[(ethane-1,2-diyl)bibenzene-2,2′-bis(methylene)]-β-thioglucoside. This reaction proceeds through a cationic Au(I)-mediated intramolecular migration of the anomeric substituent onto the alkyne moiety of the propargyl group, followed by α-attack by the hydroxy group in the glycosyl acceptor on the oxocarbenium ion. The migration of the anomeric group occurs selectively through a 6- exo - dig pathway. The 2-(phenylsulfanyl)prop-2-en-1-yl group produced during the glycosylation is removable under conditions similar to those used for removing an allyl group. This reaction will be developed for further applications in orthogonal oligosaccharide synthesis. [ABSTRACT FROM AUTHOR]