FeCl3-Catalyzed Intramolecular Michael Reaction of Styrenes for the Synthesis of Highly Substituted Indenes

A Bipyridine-Promoted Csp3 -Csp3 Coupling of beta-Chlorophenones

A novel, direct Csp³ -Csp³ coupling reaction of β-chlorophenone with alkanes using 2-(tert-butylperoxy)-2-methylpropane (DTBP) as the oxidant and 2,2'-bipyridine (bpy) as the effective additive was developed. A variety of β-chloropropiophenones were well tolerated, and afforded alkylated products in moderate to good yields. A mechanistic study indicated a free radical pathway was involved in this alkyl-alkyl cross-coupling reaction.

Racemic Total Synthesis of Elmonin and Pratenone A, from Streptomyces, Using a Common Intermediate Prepared by peri-Directed C-H Functionalization

The first total synthesis of elmonin and pratenone A, two complex rearranged angucyclinones from Streptomyces, is reported. Using peri-directed C-H functionalization, the key naphthalene fragment present in both synthetic targets was efficiently prepared. Coupling to two anisole-derived fragments gave access to the natural products, in which elmonin was prepared using a biomimetic spiro-ketalization.

Sequential Knoevenagel Condensation/Cyclization for the Synthesis of Indene and Benzofulvene Derivatives

Sequential Knoevenagel condensation/cyclization leading to indene and benzofulvene derivatives has been developed. The reaction of 2-(1-phenylvinyl)benzaldehyde with malonates gave benzylidene malonates, cyclized indenes, and dehydrogenated benzofulvenes. The product selectivity depends on the reaction conditions. The reaction with piperidine, AcOH in benzene at 80 °C for 1.5 h gave a benzylidene malonate in 75% yield as a major product. The reactions with piperidine, AcOH in benzene at 80 °C for 17 h and with TiCl₄-pyridine at room temperature gave an indene derivative in 56 and 79% yields, respectively, as a major product. The reaction with TiCl₄-Et₃N gave a benzofulvene in 40% yield selectively. Indene was transformed to a benzofulvene derivative using the reagents TiCl₄-Et₃N and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The reaction of variously substituted aryl derivatives with dimethyl malonate gave indene and benzofulvene derivatives. The reactions of 2-(1-phenylvinyl)benzaldehyde with Meldrum's acid or malononitrile also gave cyclized compounds in the suitable sequential or stepwise conditions. Furthermore, the reaction of 2-arylbenzaldehydes has been investigated. The limitation and scope have been described. The reaction mechanism of the cyclization steps has been examined by DFT calculations.

Catalytic C-C Cleavage/Alkyne-Carbonyl Metathesis Sequence of Cyclobutanones

A ring-opening/alkyne-carbonyl metathesis sequence of alkyne-tethered cyclobutanones catalyzed by AgSbF₆ is realized for the first time to furnish multisubstituted naphthyl ketones under mild conditions. A range of substrates decorated with various substituents at different positions were all well accommodated. Preliminary mechanistic studies show that silver salt acted as a Lewis acid to facilitate both C-C cleavage of the cyclobutanone moiety and the subsequent metathesis between C═O and C≡C bonds.

Cp*Co(III)-Catalyzed Ketone-Directed ortho-C-H Activation for the Synthesis of Indene Derivatives

A weakly coordinating, carbonyl-assisted C-H activation of aromatic systems with α,β-unsaturated ketone and subsequent aldol condensation has been developed using a Cp*Co(CO)I₂ catalyst. The developed method is the first example of indene synthesis by cobalt-catalyzed C-H activation. In addition, the reaction requires mild reaction conditions and easily accessible starting materials, and it shows excellent functional group compatibility.

Lewis Base-Catalyzed Enantioselective Conjugate Reduction of β,β-Disubstituted α,β-Unsaturated Ketones with Trichlorosilane: E/Z-Isomerization, Regioselectivity, and Synthetic Applications

The chiral bisphosphine dioxide-catalyzed asymmetric conjugate reduction of acyclic β,β-disubstituted α,β-unsaturated ketones with trichlorosilane affords saturated ketones having a stereogenic carbon center at the carbonyl β-position with high enantioselectivities. Because the E/Z-isomerizations of enone substrates occur concomitantly, reduction products with the same absolute configurations are obtained from either (E)- or (Z)-enones. Conjugate reduction is accelerated in the presence of an electron-rich aryl group at the β-position of the enone owing to its carbocation-stabilizing ability. Computational studies were also conducted in order to elucidate the origin of the observed enantioselectivity. The regio- and enantioselective reductions of dienones were realized and applied to the syntheses of ar-turmerone, turmeronol A, mutisianthol, and jungianol, which are optically active sesquiterpenes.

Brønsted Acid-Mediated Domino One-Pot Dual C-C Bond Formation: Chemoselective Synthesis of Fused Tricyclic Ketones

A chemoselective synthesis of fused novel tricyclic motifs via a facile domino intramolecular cyclization is presented. The strategy enables the formation of dual C-C bond via intramolecular Friedel-Crafts alkylation followed by acylation to accomplish fused tricyclic ketones. Significantly, these fused tricyclic compounds are ubiquitous and constitute major structural cores of natural products.

Gold(I)-Catalyzed Synthesis of Indenes and Cyclopentadienes: Access to (±)-Laurokamurene B and the Skeletons of the Cycloaurenones and Dysiherbols

The formal (3+2) cycloaddition between terminal allenes and aryl or styryl gold(I) carbenes generated by a retro-Buchner reaction of 7-substituted 1,3,5-cycloheptatrienes led to indenes and cyclopentadienes, respectively. These cycloaddition processes have been applied to the construction of the carbon skeleton of the cycloaurenones and the dysiherbols as well as to the total synthesis of (±)-laurokamurene B.

Facile access to functionalized indenes and fused quinolines by regioselective 5-enolexo-dig Michael addition and cyclization reactions

Herein we report a facile approach to synthesise multi-substituted indenes and cyclopenta[b]quinolines under mild conditions.