Palladium(II) Catalyzed Cyclization-Carbonylation-Cyclization Coupling Reaction of (ortho-Alkynyl Phenyl) (Methoxymethyl) Sulfides Using Molecular Oxygen as the Terminal Oxidant

Abstract

An efficient Pd II /Pd 0 -p-benzoquinone/hydroquinone-CuCl 2 /CuCl catalyst system was developed that uses environmentally friendly molecular oxygen as the terminal oxidant to catalyze the cyclization-carbonylation-cyclization coupling reaction (CCC-coupling reaction) of (o-alkynyl phenyl) (methoxymethyl) sulfides.

Cyclization–Carbonylation of 2-Alkynyl Primary Benzamides using p-Benzoquinone under Neutral Conditions

“…(Table , entry 3) 6a was obtained in 35% yield (51 mg) (ethyl acetate/hexane (1/80)) as a white solid (mp 125–127 °C) together with 3a (27% yield, 37 mg). The NMR data of the title compound was identical to those previously reported …”

“…With the optimal conditions in hand ( thiophene-2-carboxamide derivatives 2 in the cyclizationcarbonylation reaction (Table 3). First, the reactions of substrates bearing aromatic substituents in the alkyne terminus were investigated ( 9). Replacement of the aryl groups at the alkyne terminus with alkyl groups also led to the desired 6j−6l and 7e in good yields (Table 3, entries 10−12 and 20).…”

“…The NMR data of the title compound was identical to those previously reported. 9 1 H NMR (400 MHz, CDCl 3 ) δ 8.30 (ddd, J = 0.8, 1.2, 8.4 Hz, 1H), 7.98 (td, J = 0.8, 8.4 Hz, 1H), 3H),7.57 (ddd,J = 1.2,7.2,8.4 Hz,1H),3H),4.21 (s,3H), 3.72 (s, 3H); 13 C{ 1 H} NMR (100 MHz, CDCl 3 ) δ 169. 9, 160.8, 149.1, 140.3, 135.8, 131.5, 128.6, 128.5, 128.3, 126.9, 124.3, 124.0, 117.9, 117.3, 54.0, 52.3;FTIR (KBr) 2987, 2945, 1715, 1577, 1567, 1508, 1456, 1446, 1438, 1373, 1242 2 and 3 and Scheme 4) A 30 mL two-necked round-bottom flask containing a magnetic stirring bar, the substrate 1 or 2 (0.5 mmol), pbenzoquinone (82 mg, 0.75 mmol; 1.5 equiv), CH(OMe) 3 (1.0 mL, 9.1 mmol; 18 equiv), and DMSO/MeOH (2/1, 4 mL) was fitted with a rubber septum and a three-way stopcock connected to a balloon filled with carbon monoxide.…”

“…Using HC­(OMe) 3 as a dehydrating agent improved the yield slightly (Table , entries 7 and 8). Next, we investigated the reaction of 1b using the Pd­(tfa) 2 (5 mol %)/ p -benzoquinone (20 mol %)/CuCl 2 (2 mol %) catalytic system under a CO/O 2 (2/1) atmosphere (balloon) (Table , entry 9) . The reaction time increased, and the yield of 6b decreased (69%).…”

Asymmetric Cyclizative Dimerization of (ortho‐Alkynyl Phenyl) (Methoxymethyl) Sulfides with Palladium(II) Bisoxazoline Catalyst

“…The use of increased amounts of catalyst (10–14 mol %) gave good yields and enantioselectivities (entries 14 and 15). Recently, we reported the CCC‐coupling reaction of 1 using molecular oxygen as the terminal oxidant . Thus, we investigated the reaction of 1 a using the [Pd(tfa) 2 ( L11 )] (14 mol %)/ p ‐benzoquinone (10 mol %)/CuCl 2 (10 mol %) catalytic system under an oxygen atmosphere (balloon) (Table , entry 16).…”