Catalytic Asymmetric Cross‐Dehydrogenative Coupling of 2H‐Chromenes and Aldehydes

Abstract

The first catalytic asymmetric cross‐dehydrogenative coupling of 2H‐chromenes with aldehydes using o‐chloranil (3,4,5,6‐tetrachloro‐1,2‐ benzoquinone) as an oxidant has been described. The organocatalytic process is tolerated with a broad range of structurally and electronically varied 2H‐chromenes and aldehydes with good yield and high enantiocontrol.

Recent Advances in Cross‐Dehydrogenative Couplings (CDC) of C−H Bond in Aqueous Media

“…Liu and co‐workers [25] described a catalytic asymmetric CDC reaction between hydrophone and aldehydes using o ‐chloroaniline (3,4,5,6‐tetrachloro‐1,2‐benzoquinone) as the oxidant [Eq. (10)].…”

“…On the other side, PDMS sponges might provide a hydrophobic reaction microenvironment due to their inherent hydrophobicity, affording better results in water. Liu and co-workers [25] described a catalytic asymmetric CDC reaction between hydrophone and aldehydes using o-chloroaniline (3,4,5,6-tetrachloro-1,2benzoquinone) as the oxidant [Eq. 10].…”

“…Itoh and co-workers [40] developed a molecularly iodine-mediated aerobic photo-oxidative cross-dehydrogenative coupling of heteroarenes with carbonyls, activated by a catalytic amount of molecular iodine to formate C sp3 À C sp2 bonds [Eq. (25)]. The advantages of this method included mild reaction conditions, simple operation and cheap and abundant molecular iodine catalysts.…”

New Trends in Enantioselective Cross-Dehydrogenative Coupling

“…The delay in the development of the ether chemistry in contrast to the successes achieved with analogous amines has been attributed both to the higher oxidation potentials of the first, as well as to a lack of sites to which chiral catalysts can coordinate. Then, L. Liu and coworkers developed a procedure to couple 2H-chromenes and aldehydes, thinking of the potential of the products, enantiopure α-substituted 2H-chromenes, structural components of many biologically active natural products and pharmaceuticals with many types of activities [57]. This new procedure, catalyzed by a chiral imidazolidinone in the presence of LiOTf, used o-chloranil as the oxidant.…”

Diastereoselective Generation of C2-Azlactonized 2H-Chromenes via Brønsted Acid-Catalyzed Oxo-Cyclization of Propargyl Alcohols

“… , Moreover, 2 H -chromene derivatives have demonstrated wide applications in photochromic materials and behaved as precursors to flavylium dyes for preparing solar cells and optical memories . Due to their significant utility, extensive efforts have been devoted to establishing state of the art and reliable methods for fabricating 2-substituted 2 H -chromenes over past decades, including traditional annulations of phenol or salicylaldehyde derivatives, nucleophilic substitutions of chromene acetals, C–H functionalizations of 2 H -chromene skeletons, and [4 + 2] annulation of alkynyl thioethers . Despite the great advances that have occurred, the continuous development of catalytic and versatile synthetic strategies that allow the direct formation of new C2-functionalized 2 H -chromenes with three-dimensionality could have a significant influence on the discovery of new lead compounds.…”