Palladium-catalyzed [2 + 2 + 1] annulation: access to chromone fused cyclopentanones with cyclopropenone as the CO source

Abstract

Herein we report a palladium-catalyzed [2+2+1] annulation among 3-iodochromones, bridged olefins, and cyclopropenone, giving a variety of chromone fused cyclopentanones that are of interest in medicinal chemistry. This protocol involves...

Diazotrifluoroethyl Radical: A CF3-Containing Building Block in [3 + 2] Cycloaddition

“…As shown in Figure a, CF 3 CHN 2 , with three resonance structures ( A , B , and C ), is a versatile building block widely used as a metal carbene precursor, 1,3-dipole, C -nucleophile, and N -electrophile. Compared with the extensively utilized CF 3 CHN 2 , the diazotrifluoroethyl radical [ D , CF 3 C­(·)­N 2 ], the trifluoroethylcarbyne (CF 3 CĊ:) equivalent from hypervalent iodine­(III) reagent 2 pioneered by Suero in 2018, remains rarely exploited (Figure b). − With our continuing interest in the assembly of fluorine-containing molecules and heterocycles, we wondered if [CF 3 C­(·)­N 2 ] could act as an unusual CF 3 -containing building block for the construction of CF 3 -containing heterocycles.…”

Toward the Generation of 2-Amino-3-Formyl Difunctionalized Chromones via Pd-Enabled Rearrangement Strategy

“…However, the reaction of 16 under the standard conditions failed to give product 3a (Scheme 7a), 25 indicating that the amide was not the intermediate for this transformation. Subsequently, the observation of the 18 O-labeled product in the presence of H 2 O 18 rationalized that the oxygen atom in formyl group came from H 2 O of the reaction system (Scheme 7b), which supports the nucleophilic ring-opening of benzo-γpyrone moiety by HO − and the involvement of phenoxy anion D (Figure 1f). In addition, the nondeuterated formyl group was detected with D 2 O instead of H 2 O (Scheme 7c).…”

“…Hence, exploration of a novel strategy toward the syntheses of chromone derivatives, especially the multifunctionalized chromones, is highly desirable. Considering the character of ring-opening of isoflavones to form the phenoxy anion under basic conditions (Figure e) and the unique properties of isocyanides in organic synthesis as well as our continuous interest in the elaboration of chromonyl-norbornyl-palladacycle intermediate for the construction of various chromone derivatives, − we wondered if the phenoxy anion intermediate could be engaged in a ring-closure reaction under palladium-catalyzed conditions, delivering the functionalized chromones, rather than undergoing a competitive decarboxylation event, thus generating the undesired ketone byproduct. Herein, we report our most recent endeavor on the molecular rearrangement of 3-halogenochromones based on functional group transformation; this protocol provides a seemingly direct ortho -C–H amination and ipso -formylation of 3-halogenochromones with isocyanides enabled by palladium catalysis under basic conditions (Figure f).…”

Heterocycles from cyclopropenones

“…Zhu et al in 2021, have developed a palladium-catalyzed three-component reaction of substituted iodochromen-4-ones 105a–h , (1 R ,4 S )-bicyclo[2.2.1]hept-2-ene ( 106 ) and 1b in fluorobenzene in the presence of tris-(4-trifluoromethyl-phenyl)phosphine P(4-CF 3 -C 6 H 4 ) 3 at 100 °C for 24 h. (6 aR ,7 S ,10 R ,10 aS )-6 a ,7,8,9,10,10 a -Hexahydro-7,10-methanoindeno[2,1- b ]chromene-6,11-diones 107a–h were obtained in 65–70% yield (Scheme 66). 108…”