A unified approach to the daucane and sphenolobane bicyclo[5.3.0]decane core: enantioselective total syntheses of daucene, daucenal, epoxydaucenal B, and 14-para-anisoyloxydauc-4,8-diene

Synthesis of Unsymmetrical 1,6-Dicarbonyl Compounds through Photocatalytic One-Pot Tandem Three-Component Reaction

Unsymmetrical 1,6-dicarbonyl compounds are useful building blocks in organic synthesis. However, the synthetic methods are limited. Herein we report a three-component one-pot reaction for the synthesis of unsymmetrical 1,6-diketones. This reaction utilizes sulfides as radical precursors and enol ethers as building blocks. It takes advantage of photocatalysis and Lewis acid catalysis. Its synthetic utility was demonstrated in the modification of biorelevant compounds.

Total Syntheses and Absolute Configuration Assignment of (+)-Sootepdienone, (-)-Jambolanin C, (-)-Jambolanin I, and (-)-Gibberodione

Total syntheses of the sesquiterpenes (+)-sootepdienone, (-)-jambolanin C, (-)-jambolanin I, and (-)-gibberodione have been accomplished in 10 steps each from R-(+)-pulegone, allowing assignment of the absolute configuration of the natural products. A key step in the synthetic pathways involves the one-carbon ring expansion of a cyclic allylic phosphonate to a substituted cycloheptenone by a tandem oxidative cleavage/intramolecular Horner-Wadsworth-Emmons reaction.

Total syntheses of (±)-penicibilaenes A and B via intramolecular aldol condensation

Concise total syntheses of penicibilaenes A and B were achieved via intramolecular aldol condensation and other key reactions.

Applications of Transition-Metal-Catalyzed Asymmetric Allylic Substitution in Total Synthesis of Natural Products: An Update

Metal-catalyzed asymmetric allylic substitution (AAS) reaction is one of the most synthetically useful reactions catalyzed by metal complexes for the formation of carbon-carbon and carbon-heteroatom bonds. It comprises the substitution of allylic substrates with a wide range of nucleophiles or S_N 2'-type allylic substitution, which results in the formation of the above-mentioned bonds with high levels of enantioselective induction. AAS reaction tolerates a broad range of functional groups, thus has been successfully applied in the asymmetric synthesis of a wide range of optically pure compounds. This reaction has been extensively used in the total synthesis of several complex molecules, especially natural products. In this review, we try to highlight the applications of metal (Pd, Ir, Mo, or Cu)-catalyzed AAS reaction in the total synthesis of the biologically active natural products, as a key step, updating the subject from 2003 till date.

Access to Natural Valparanes and Daucanes: Enantioselective Synthesis of (-)-Valpara-2,15-diene and (+)-Isodaucene

The first total synthesis of a natural diterpene valparane, (-)-valpara-2,15-diene (1), has been achieved from all -trans-geranylgeraniol (9), a natural renewable compound. The key steps involve a Ti(III)-mediated radical cyclization of the chiral monoepoxypolyene (14 R,15 R)-14,15-epoxy,16- tert-butyldimethylsilyloxygeranyllinalyl acetate (8) to give the 6,6,7-tricyclic intermediate 7 with stereocontrolled formation of six stereocenters; a stereo- and regio-directed contraction of the A ring in 7 to produce a cyclopentane ring; and the ready generation of the target isopropenyl group. This research provides access to structurally related natural products such as the sesquiterpene (+)-isodaucene (3), the synthesis of which is also reported herein.

Synthesis of carotol using a formal (4+1)-cycloaddition of chiral dialkoxycarbenes

We report formal intramolecular (4+1)-cycloadditions of dialkoxycarbenes used in the synthesis of the daucane-type sesquiterpene carotol. We found a chiral dialkoxycarbene capable of diastereoselective formation of a key oxabicyclo[3.3.0]octene adduct. Carotol was synthesized in 14 linear steps from simple starting materials.

Photochemical Approaches to Complex Chemotypes: Applications in Natural Product Synthesis

The use of photochemical transformations is a powerful strategy that allows for the formation of a high degree of molecular complexity from relatively simple building blocks in a single step. A central feature of all light-promoted transformations is the involvement of electronically excited states, generated upon absorption of photons. This produces transient reactive intermediates and significantly alters the reactivity of a chemical compound. The input of energy provided by light thus offers a means to produce strained and unique target compounds that cannot be assembled using thermal protocols. This review aims at highlighting photochemical transformations as a tool for rapidly accessing structurally and stereochemically diverse scaffolds. Synthetic designs based on photochemical transformations have the potential to afford complex polycyclic carbon skeletons with impressive efficiency, which are of high value in total synthesis.

Revisiting the Male-Produced Aggregation Pheromone of the Lesser Mealworm, Alphitobius diaperinus (Coleoptera, Tenebrionidae): Identification of a Six-Component Pheromone from a Brazilian Population

The lesser mealworm, Alphitobius diaperinus Panzer 1797 (Coleoptera: Tenebrionidae), is a cosmopolitan insect pest affecting poultry production. Due to its cryptic behavior, insecticide control is usually not efficient. Thus, sustainable and effective methods would have an enormous and positive impact in poultry production. The aim of this study was to confirm the identity of the male-produced aggregation pheromone for a Brazilian population of A. diaperinus and to evaluate its biological activity in behavioral assays. Six male-specific compounds were identified: (R)-limonene (1), (E)-ocimene (2), 2-nonanone (3), (S)-linalool (4), (R)-daucene (5), all described before in an American population, and a sixth component, (E,E)-α-farnesene (6), which is apparently exclusive to a Brazilian population. Y-Tube bioassays confirmed the presence of a male-produced aggregation pheromone and showed that all components need to be present in a similar ratio and concentration as emitted by male A. diaperinus to produce a positive chemotactic response.

Dialkoxycarbenes in (4 + 1) Cycloadditions: Application to the Synthesis of Carotol

Dialkoxycarbenes are more reactive than NHCs and participate in many reactions including a formal (4 + 1) cycloaddition with electron-deficient dienes. We have learned to control the relative stereochemistry of the newly created chiral carbons in this process and now report that, combined with a chiral auxiliary, it has been used successfully in a short and efficient synthesis of the sesquiterpene carotol.