First example of samarium diiodide-promoted sequential cyclization and ring-expansion reactions of α-bromomethyl cyclic β-keto esters to homologated γ-keto esters

Organic dye-catalyzed radical ring expansion reaction

Herein, we reported an attractive method for synthesizing medium-sized rings that are catalyzed by erythrosine B under fluorescent light irradiation. This synthetic approach featured mild conditions, a facile procedure, a broad substrate scope, and moderate-to-good yields.

Herein, we reported an attractive method for synthesizing medium-sized rings that are catalyzed by erythrosine B under fluorescent light irradiation.

Synthetic efforts toward cyathane diterpenoid natural products

Covering: 2000 to 2008. Previous review: D. L. Wright and C. R. Whitehead, Org. Prep. Proced. Int., 2000, 32, 309-330. An overview of synthetic efforts toward cyathane diterpenoid natural products from the year 2000 to present is provided. The emphasis of this review is the various ring-constructing and stereoforming strategies employed in these synthetic routes.

Samarium diiodide mediated reactions in total synthesis

Introduced by Henri Kagan more than three decades ago, samarium diiodide (SmI(2)) has found increasing application in chemical synthesis. This single-electron reducing agent has been particularly useful in C-C bond formations, including those found in total synthesis endeavors. This Review highlights selected applications of SmI(2) in total synthesis, with special emphasis on novel transformations and mechanistic considerations. The examples discussed are both illustrative of the power of this reagent in the construction of complex molecules and inspirational for the design of synthetic strategies toward such targets, both natural and designed.

Enantioselective total synthesis of (-)-erinacine B

The first enantioselective total synthesis of (-)-erinacine B has been achieved. Our approach features convergent construction of the 5-6-7 tricyclic cyathane core system via chiral building blocks prepared using asymmetric catalysis developed by us and highly stereoselective construction of all stereogenic centers in the aglycon. [reaction: see text].

Expedient Construction of the Vibsanin E Core without the Use of Protecting Groups

[reaction: see text] The tricyclic core of vibsanin E was constructed without the use of a protecting group in six steps. The El Gaïed Baylis-Hillman variant was key to allowing the Brønsted acid induced tandem cyclization forming rings B and C in one operation.

Synthetic Studies on Cyathins: Enantioselective Total Synthesis of (+)-Allocyathin B2

[reaction: see text] The enantioselective total synthesis of (+)-allocyathin B(2) has been achieved. Our approach features a convergent enantioselective construction of the 5-6-7 tricyclic core system using the originally developed chiral building blocks via asymmetric catalysis, the intramolecular aldol reaction in high yield, successful samarium diiodide-mediated ring expansion, and a newly developed double-bond installation method.

Zinc- and Indium-Mediated Ring-Expansion Reaction of α-Halomethyl Cyclic β-Keto Esters in Aqueous Alcohol

Radical ring-expansion reaction of various alpha-halomethyl cyclic beta-keto esters and alpha-halomethyl benzocyclic beta-keto esters and chain-extension reaction of alpha-halomethyl beta-keto esters with zinc powder and indium powder in refluxing aqueous alcohol were carried out to generate the corresponding ring-expansion and chain-extension products. As the results indicate, it was found zinc powder was more effective than indium powder to give the corresponding ring-expanded products in quite good yields. Moreover, the addition of zinc bromide as Lewis acid showed an increase of the yields, depending on the substrates. The present reaction conditions are highly effective, simple, and environmentally friendly.

Total synthesis of the cyathane diterpenoid (+/-)-sarcodonin G

[process--see text] The total synthesis of (+/-)-sarcodonin G (3), a highly functionalized member of the cyathane family of diterpenoids, is described.