Effective Chirality Transfer in [3+2] Reaction between Allenyl-Rhodium and Enal: Mechanistic Study Based on DFT Calculations

The Total Synthesis of Diquinane-Containing Natural Products

Diquinane or bicyclo[3.3.0]octane is a conspicuous structural unit existing in the carbo-frameworks of a wide range of natural products such as alkaloids and terpenoids. These diquinane-containing molecules not merely exhibit intriguing architectures, but also showcase a broad spectrum of significant bioactivities, which draw widespread attention from the global synthetic community. During the past decade, with an aim to accomplish the total syntheses of such specified cornucopias of natural products, a variety of elegant strategies for construction of the diquinane ring system have been disclosed. In this Minireview, the achievements on this subject in the timeline from 2010 to June 2020 are demonstrated and it is discussed how the diquinane unit is strategically forged in the context of the specific target structure. In addition, impacts of the selected works to the field of natural product total synthesis is highlighted and the particular outlook of diquinane-containing natural product synthesis is provided.

Carbon-Carbon Bond Cleavage at Allylic Positions: Retro-allylation and Deallylation

The development of C-C bond-cleaving transformations is an issue in modern organic chemistry that is as challenging as it is important. Among these transformations, the retro-allylation and deallylation of allylic compounds are uniquely intriguing methods for the cleavage of C-C σ bonds at the allylic position. Retro-allylation is regarded as a prospective method for the generation of highly valuable regio- and stereodefined allylic metal compounds. Because the C-C cleavage proceeds via a favorable six-membered chairlike transition state, the regio- and stereochemical information on the starting homoallylic alcohols can be transferred onto the products. Moreover, retro-allylation can also be achieved using enantioselective C-C cleavage powered by chiral catalysts for the synthesis of enantiomerically enriched compounds. As a result of these attractive features, retro-allylation has wide utility in regio-, stereo-, and enantioselective synthesis. Deallylation is C-C σ-bond cleavage involving the departure of an allylic fragment and the formation of a relatively stable carbanion or radical, and it proceeds via either oxidative addition to a low-valent metal or an addition/β-elimination cascade. The removal of the versatile allylic group might seem to be unproductive; however, this unique transformation offers the opportunity of using the allylic group as a protective group for acidic C-H bonds. This Review aims to exhibit the synthetic utility as well as the uniqueness of these two C-C σ-bond cleavage methods by presenting a wide range of transformations of allylic compounds with the aid of main group metals, transition-metal catalysts, and radical species.

Retro-metal-ene versus retro-Aldol: mechanistic insight into Rh-catalysed formal [3+2] cycloaddition

Theoretical calculations have been performed to investigate the mechanism and stereoselectivity of rhodium-catalysed intramolecular [3+2] cycloaddition for construction of a substituted hexahydropentalene complex. A new C-C bond cleavage mechanism, retro-Aldol-type, is proposed and verified for this Rh-catalysed [3+2] cycloaddition reaction.

Long distance unconjugated agostic-assisted 1,5-H shift in a Ru-mediated Alder-ene type reaction: mechanism and stereoselectivity

A long distance unconjugated novel 1,5-H shift mechanism for a Ru-catalyzed Alder-ene type alkene–alkyne coupling reaction was examined by DFT.

C–H bond cleavage occurring on a Rh(v) intermediate: a theoretical study of Rh-catalyzed arene azidation

Our theoretical calculations indicated that the oxidation of Rh(iii) to Rh(v) by PhI(OAc)OTs is a facile process. Subsequent electrophilic deprotonation was shown to occur from a Rh(v) intermediate rather than a Rh(iii) intermediate.

Insights into disilylation and distannation: sequence influence and ligand/steric effects on Pd-catalyzed difunctionalization of carbenes

Density functional theory (DFT) calculation has been used to reveal the mechanism of Pd-catalyzed disilylation of carbene, which is a pathway to construct disilylmethane derivatives.

Formal Total Synthesis of (±)-Lycojaponicumin C

The formal total synthesis of (±)-lycojaponicumin C has been accomplished. Key transformations include a Rh-catalyzed formal [3 + 2] cycloaddition reaction to construct the bicyclic [3.3.0] scaffold bearing two vicinal quaternary carbon centers, a stereoselective γ-hydroxyl directed Michael addition to introduce the vinyl group at a bulky position, and a late-stage ring-closing metathesis reaction to form the cyclohexanone ring.