Total synthesis of (±)-Δ9(12)-capnellene

Photochemical reactions as key steps in natural product synthesis

Photochemical reactions contribute in a significant way to the existing repertoire of carbon-carbon bond-forming reactions by allowing access to exceptional molecular structures that cannot be obtained by conventional means. In this Review, the most important photochemical transformations that have been employed in natural product synthesis are presented. Selected total syntheses are discussed as examples, with particular attention given to the photochemical key step and its stereoselectivity. The structural relationship between the photochemically generated molecule and the natural product is shown, and, where necessary, the consecutive reactions in the synthesis are illustrated and classified.

Generation and trapping of cyclopentenylidene gold species: four pathways to polycyclic compounds

Cyclopentenylidene gold complexes can easily be formed from vinyl allenes through a Nazarov-like mechanism. Such carbenes may transform in four different ways into polycyclic frameworks: electrophilic cyclopropanation, C-H insertion, C-C migration, or proton shift. We have studied the selectivity of these different pathways and used our findings for the expedient preparation of valuable complex molecules. An application to the total synthesis of a natural product, Delta(9(12))-capnellene, is presented. DFT computations were carried out to shed light on the mechanisms.

Microbial Baeyer-Villiger reaction of bicyclo[3.2.0]heptan-6-ones--a novel approach to sarkomycin A

Racemic (1 alpha, 2 alpha, 5 alpha)- and (1 beta, 2 alpha, 5 beta)-2- bromobicyclo[3.2.0]heptan-6-one (rac-7, rac-10, respectively), (1 alpha, 2 alpha, 5 beta)- and (1 beta, 2 alpha, 5 beta)-2- benzyloxybicyclo[3.2.0]heptan-6-one (rac-15, rac-13, respectively), (1 beta, 2 alpha, 5 beta)-2-hydroxybicyclo[3.2.0]heptan-6-one (rac-17) and cis-bicyclo[3.2.0]hept-2-en-7-one (rac-18) were subjected to a microbial Baeyer-Villiger reaction by Acinetobacter calcoaceticus NCIB 9871. In each case both regioisomeric lactones were formed (67-93% yield) having always the opposite configuration (20 to > 99 % e.e.). Both the ratio of the regioisomers and the enantiomeric excess proved to be dependent on the type of substitution. Analogously cis-bicyclo[3.2.0]heptan-2,6-dione (rac-1) gave besides other products cyclosarkomycin (1b) (7 % yield, 97 % e.e.). Compound 1b was also obtained from the Baeyer-Villiger product of rac-17 by Swern oxidation (total yield starting from rac-17 9 %, > 98 % e.e.).