A Domino Palladium-Catalyzed C–C and C–O Bonds Formation via Dual O–H Bond Activation: Synthesis of 6,6-Dialkyl-6H-benzo[c]chromenes

Abstract

An efficient Pd-catalyzed domino reaction of α,α-dialkyl-(2-bromoaryl)methanols to 6,6-dialkyl-6H-benzo[c]chromenes is presented. Their formation can be explained via a five membered Pd(II)-cycle that efficiently involves a domino homocoupling with the second molecule, β-carbon cleavage, and finally intramolecular Buchwald-Hartwig cyclization. This domino process effectively involves breaking of five σ-bonds (2C-Br, 2O-H, and a C-C) and formation of two new σ-bonds (C-C and C-O). This mechanistic pathway is unprecedented and further illustrates the power of transition metal catalysis.

From catechol‐tocopherol to catechol‐hydroquinone polyphenolic antioxidant hybrids

“…The combined organic layers are dried over Na 2 SO 4 , filtered, and concentrated in vacuum. The crude product is purified by column chromatography (eluent DCM/EtOAc = 3/1) to yield the desired product as an orange oil (365 mg, 81%) used without further purification in the next step [20] . 1 H‐NMR, 400 MHz: 7.27 (s, 1H); 7.02(s, 1H); 3.86 (s, 3H); 3.85 (s, 3H); 1.72 (s, 6H) ppm.…”

The study of metal-free and palladium-catalysed synthesis of benzochromenes via direct C–H arylation using unactivated aryl benzyl ethers derived from essential oils as raw materials

“…First, the reaction between 8a in the presence of the catalyst Pd(OAc) 2 (5 mol%)/PPh 3 (5 mol%) and base Cs 2 CO 3 (2 equiv.) in DMF at 80°C for 48 h, avoiding the use of any additive, 30 did not furnish the desired product ( conditions lead to the complete recovery of the starting material ( Table 2, entry 2). A change of Pd-catalyst for others from Pd(OAc) 2 under the same parameters did not show any effect in the conversion of 8a into 9 ( Table 2, entries 3 and 4).…”

Reagent‐Controlled Cyclization–Deprotection Reaction to Yield either Fluorenes or Benzochromenes

“…Several methods have been reported for the synthesis of the benzochromene backbone. More recent methods use cyclotrimerization,8 palladium‐catalysed cyclization of homocoupled intermediates,9 carbonyl insertion under Schlenk conditions,10 or multicomponent synthesis 11. Syntheses of fluorenes have previously been reported using Brønsted acids,12 Lewis acids,12,13 photodehydration,13 photocyclization,14 or precious transition‐metal complexes 15…”