C-O formation

Several natural products, as well as many versatile synthetic intermediates, have a carbon-oxygen bond at the a-position of the carbonyl compound. Therefore, synthetic strategies aiming to perform the stereoselective introduction of this carbon-oxygen bond are of great importance, and several organocatalytic methods have been developed recently. 

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Two types of substrate probe, cis- and trans-l,3-dimethylcyclopentane and ethyl- and 2-propylcyclopropane, were used to shed light on mechanishc details of the hydroxylahon step [30]. In the use of the first two probes, the participation of Ti—OOH species in a concerted mechanism would predict either the retention or the inversion of configurahon at the chiral center, while the stereochemistry of a homolytic mechanism would be determined by the compehhon between the epimerization of the transient terhary carbon radical and C—O formation (Scheme... 

The data presented here unlock the mystery of how fullerenes appear near C30 in laser desorption experiments when no graphitic building blocks are present at smaller sizes. The ring fullerene isomerization mechanism might also help explain the rather surprising propensity for C o formation in carbon arc rectors. ... 

Methods for lactone synthesis by transition metal catalysis involving C—O formation developed over the past 50 years have demonstrated much promise. Indeed, lactones have inspired the discovery of new organometallic transformations, design of metal catalysts, and detailed understanding of reaction mechanisms. Issues of waste minimization and stereoselectivity have been addressed. Future developments for chiral lactone synthesis will likely focus on establishing efficient transformations with broad scope and application in complex molecule total synthesis, especially in regards to macrolactonization where entropic costs often plague intramolecular reactivity with undesired intermolecular reactions. 

Scheme 3.1 General pathways for the synthesis of oxacycles. (a) C-H activation/C-O formation and (b) C-H activation/C-C formation.

Palladium-Catalyzed C-H Activation/C-O Formation to Construct Oxacycles I 83... 

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