Carbon-Carbon and Carbon Heteroatom Bond Forming Reactions: From Organocatalysts to Quantum Dots

Abstract

Butenolides containing stereogenic centers on the ring, are commonly encountered structural motifs, found in many natural products. Consequently, there has been considerable interest in efficient and stereoselective synthesis of functionalized butenolides. The installation of an unfunctionalized allyl group on the unactivated butenolides in regio- and enantioselective fashion, constitutes a serious challenge and at the same time has the potential to generate densely functionalized molecular architectures. In conclusion, we have demonstrated the ability of CdSe nanocrystals to sensitize the visible light mediated aerobic oxidation of boronic acids. This general and mild protocol allows for the efficient oxidation of both aromatic as well as aliphatic boronic acids for the synthesis of phenols and aliphatic alcohols in good to excellent yields. Requirement of low catalyst loading (down to 10 ppm) combined with excellent photostability of the QDs helped us achieving outstanding turnover numbers (>62000) even in the domain of photoredox catalysis. We further show that this reaction occurs via an initial rapid (~350 ps) electron transfer from the photoexcited QDs, followed by the abstraction of the hole. Considering the mildness and functional group tolerance, we expect our protocol to be applicable for the late-stage hydroxylation in complex syntheses. Quantum dots have already gained considerable interest as an efficient photosensitizer to catalyze organic transformations. Although, various protocols have been developed to forge either carboncarbon or carbon-heteroatom bond, it has not been applied for any enantioselective transformation so far. Our future aim would be to develop an enantioselective organic transformation using QDs as a photocatalyst in combination with a chiral catalyst