Probing competitive pathways in building a hydroazulene moiety by reductive cyclization

Electrochemically Enabled Total Syntheses of Natural Products

Electrochemical techniques have helped to enable the total synthesis of natural products since the pioneering work of Kolbe in the mid 1800's. The electrochemical toolset grows every day and these new possibilities change the way chemists look at and think about natural products. This review provides a perspective on total syntheses wherein electrochemical techniques enabled the carbon─carbon bond formations in the skeletal assembly of important natural products, discussion of mechanistic details, and representative examples of the bond formations enabled over the last several decades. These bond formations are often distinctly different from those possible with conventional chemistries and allow assemblies complementary to other techniques.

The isolation and synthesis of neodolastane diterpenoids

This account summarises the progress in isolation, characterisation and synthesis of diterpenoids sharing a tricyclic neodolastane skeleton as well as their biogenetic origin and diverse biological activities.

Small molecule natural products in the discovery of therapeutic agents: the synthesis connection

Natural products have been a rich source of agents of value in medicine. They have also inspired, at various levels, the fashioning of nonnatural agents of pharmaceutical import. Hitherto, these nonnatural derivatives have been primarily synthesized by manipulating the natural product. As a consequence of major innovations in the subscience of synthetic methodology, the capacity of synthesis to deal with molecules of considerable complexity has increased dramatically. In this paper, we show by example some total syntheses which draw from strategy-enabling advances in methodology. Moreover, we show how these capabilities can be used to discover and develop new agents of potential pharmaceutical value without recourse to the natural product itself.

Total synthesis of guanacastepene a: a route to enantiomeric control

[reaction: see text] The goal of the total synthesis of guanacastepene A served as a focus to bring together several chemical inquiries. One involved the synthesis of fused 5,7-hydrazulenones (see structure 20). Another issue had to do with the mechanistic intermediates in reductive cyclizations (see 17 to 18 and 19). The total synthesis required a mastery of an intramolecular Knoevenagel condensation of a beta,gamma-unsaturated ketone (see compound 41). Actually, cyclization was best accomplished when the terminal double bond of 41 was first converted to an epoxide. Further issues related to the stereochemistry at C5 and, rather surprisingly, the propensity for beta-face acetoxylation at C13. Crystallographic verification of the assigned beta-stereochemistry at C13 is provided. Finally, a route to optically active material is provided (see compound 20). A key element in this construction was an enantioselective addition of isopropenyl cuprate to 2-methylcyclopentenone (see compound 99).

An Electrochemical Approach to the Guanacastepenes

An asymmetric approach toward the [6-7-5] ring system of the guanacastepenes is described. [structure: see text]