Synthesis and stereochemistry of a saturated tricyclic taxane model

Catalyst-free visible light-promoted defunctionalization of alkyl isocyanides with a hydrosilane through C-N bond cleavage

A radical initiator-free defunctionalization reaction of alkyl isocyanides with a hydrosilane has been established through C-N bond cleavage under catalyst-free visible light irradiation. Various alkyl isocyanides participated in the defunctionalization with tris(trimethylsilyl)silane under blue light irradiation at room temperature, delivering the reduced products in good yields with high chemoselectivity.

Strategies and Lessons Learned from Total Synthesis of Taxol

Taxol (paclitaxel), the most well-known taxane diterpenoid, is the best-selling natural-source anticancer drug ever produced and one of the most common prescriptions in the treatment of breast, lung, and ovarian cancers, saving countless lives around the world. Structurally, Taxol possesses a highly oxygenated [6-8-6-4] core bearing 11 stereocenters, seven of which are contiguous chiral centers. Moreover, the extremely strained bicyclo[5.3.1] undecane ring system with a bridgehead double bond is a unique structural feature. All these features make Taxol a highly challenging synthetic target. Tremendous synthetic efforts from more than 60 research groups around the world have already culminated in ten total syntheses and three formal syntheses, as well as more than 60 synthetic model studies of Taxol. This review is intended to provide a long-overdue appraisal of the great achievements in the total syntheses of Taxol reported in the last few decades. In doing so, we summarize the development of synthesis toward Taxol from 1994 to 2022, including the evolution of synthetic strategy for accessing this complex molecular scaffold and key lessons learned from such endeavors. Finally, we briefly discuss the future of the research in this area.

Strain Release Chemistry of Photogenerated Small-Ring Intermediates

Photochemical processes, such as isomerizations and cycloadditions, have proven to be very useful in the construction of highly strained molecular frameworks. Photoinduced ring strain enables subsequent exergonic reactions which do not require the input of additional chemical energy and provides a variety of attractive synthetic options leading to complex structures. This review covers the progress achieved in the application of sequences combining excitation by ultraviolet light to form strained intermediates, which are further transformed to lower energy products in strain-release reactions. As ring strain is considerable in small ring systems, photogenerated three- and four-membered rings will be covered, mainly focusing on examples from 2000 to May 2020.

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.

Stereoselective Synthesis of the Taxane Ring System via the Tandem Diels-Alder Cycloaddition

The application of the tandem Diels-Alder cycloaddition to the stereoselective synthesis of the tricyclic ring system of the taxane diterpenes is described. The exceedingly direct, two-step synthesis of the B/C cis-fused taxane nucleus in 50% overall yield from the reaction of two readily available acyclic precursors underscores the efficiency of this approach. A critical feature of the second, intramolecular Diels-Alder cyclcoaddition is the transmission of stereochemical information across the taxane framework, i.e., from the C ring to the A ring. The cycloaddition of both cis- and trans-disubstituted C ring constructs leads to the establishment of the requisite C-1/C-3 relative stereochemistry for the synthesis of taxanes. A computational model is presented to account for the high levels of asymmetric induction observed in these reactions.