Synthesis of Flavanones via Palladium(II)-Catalyzed One-Pot β-Arylation of Chromanones with Arylboronic Acids

Abstract

A total of 47 flavanones were expediently synthesized via one-pot β-arylation of chromanones, a class of simple ketones possessing chemically unactivated β sites, with arylboronic acids via tandem palladium­(II) catalysis. This reaction provides a novel route to various flavanones, including natural products such as naringenin trimethyl ether, in yields up to 92%.

Transfer Hydrogenation of Flavanones and ortho‐Hydroxychalcones to 1,3‐Diarylpropanols Catalyzed by CNN Pincer Ruthenium Complexes

“…[7] The lack of general and efficient methods for the preparation of ortho-hydroxy 1,3-diarylpropanols, prompted us to develop an alternative procedure via catalytic reduction of flavanones and ortho-hydroxychalcones, which are accessible from natural sources or can be easily synthesized following diverse approaches, including aldol condensation between ortho-hydroxyacetophenones and benzaldehydes in basic media and further cyclation [16,17] and arylation of chromanones with arylboronic acids in the presence of a palladium catalyst. [18] Employment of well-defined homogeneous catalysts has been demonstrated crucial for achieving high selectivity in several organic transformations, [19] reducing the formation of by-products and waste. [20] The transfer hydrogenation (TH) [21][22][23][24][25] of carbonyl compounds catalyzed by ruthenium(II) complexes [26] is a well-established way for the preparations of (chiral) alcohols by using 2-propanol as hydrogen donor.…”

Catalytic β-Functionalization of Carbonyl Compounds Enabled by α,β-Desaturation

“…In 2019, Kim and co-workers reported the synthesis of flavanones from the Pd-catalyzed β-arylation of chromanones with arylboronic acids (see Scheme 10). 34 While both α,βdesaturation and conjugate addition steps were catalyzed by Pd, addition of arylboronic acids in a sequential fashion after completion of the α,β-desaturation process was crucial for better yields and minimal overoxidation (generating flavone). Trifluoroacetic acid was also found beneficial for suppressing overoxidation.…”

A Novel Approach to N‐Tf 2‐Aryl‐2,3‐Dihydroquinolin‐ 4(1H)‐ones via a Ligand‐Free Pd(II)‐Catalyzed Oxidative Aza‐Michael Cyclization

“…Recently, we developed the palladium(II)‐catalyzed one‐pot β ‐arylation of chromanones, a kind of simple and tolerable ketones, with arylboronic acids via a dehydrogenation/conjugate sequence for the synthesis of flavanones (Scheme 1). [12] Based on our previous study, we herein report a novel approach to synthesize N ‐Tf 2‐aryl‐2,3‐dihydroquinolin‐4(1 H )‐ones from manageable N ‐Tf‐2′‐aminodihydrochalcones via Pd(II)‐catalyzed dehydrogenation followed by intramolecular aza‐Michael addition. In particular, the attractive features of this method include the in situ formation of 2′‐aminochalcones for 1,4‐addition using Pd(TFA) 2 without ligands under mild conditions.…”

“…A plausible mechanism involving the dehydrogenation/aza‐Michael cyclization sequence for the synthesis of N ‐Tf 2‐phenyl‐2,3‐dihydroquinolin‐4(1 H )‐one 2 b is illustrated in Scheme 2. Based on our prior mechanistic studies, [12] it is plausible that N ‐Tf‐2′‐aminodihydrochalcone 1 b might react with Pd(II)X 2 to form Pd(II) complex I via C–H palladation [14] . β ‐Hydride elimination of I delivers a key intermediate, N ‐Tf‐2′‐aminochalcone 4 b , accompanied by HPd(II)X which undergoes reductive elimination to afford the Pd(0) species [15] .…”