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33.4.17.1.3.2 Method 2: Isomerizing Heck Reactions of 2,5-Dihydropyrroles

DOI: 10.1055/sos-SD-033-00633

Jubault, P.; Leclerc, E.; Quirion, J.-C.Science of Synthesis, (200733593.

The regioselective, palladium-catalyzed arylation reaction of N-substituted 2,5-dihydropyrrole 36 is an excellent way to prepare 3-aryl-2,3-dihydropyrroles, which are key intermediates in the synthesis of 3-arylpyrrolidines. The initial Heck arylation experiments[‌44‌] were conducted using iodobenzene as the arylating reagent. Arylation of methyl 2,5-dihydropyrrole-1-carboxylate (36) with iodobenzene, using a catalytic amount palladium(II) acetate with 1,3-bis(diphenylphosphino)propane as the phosphine ligand, and N,N-diisopropylethylamine as base, in dimethylformamide at 100°C, results in a reaction mixture comprised of methyl 3-phenyl-2,3-dihydropyrrole-1-carboxylate (37, Ar1=Ph), methyl 2-phenyl-2,3-dihydropyrrole-1-carboxylate (38, Ar1=Ph), and 1-(methoxycarbonyl)-2,4-diphenyl-2,5-dihydropyrrole (39, Ar1=Ph) as the major products, all formed in yields higher than 10% (Scheme 16). In addition, a considerable amount of 36 isomerizes to the enamide 40. The compounds 3740 (Ar1=1-naphthyl) are also the major components, together with the deoxygenated naphthalene, when 1-naphthyl trifluoromethanesulfonate is employed under similar conditions. The naphthyl derivatives 37 (Ar1=1-naphthyl) and 38 (Ar1=1-naphthyl) are formed in equal amounts. Several additives have been studied to minimize the amount of isomerized enamide 40.

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Me8 M Meeee (%) Mee
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Meeeeeeeeee 88

Me8 Meeee (%) Mee
Me 88 [‌88‌]
8-eeeeeeee 88 [‌88‌]
8-eeeeeeee 88 [‌88‌]
8-eeeeeee 88 [‌88‌]
8-MeM8M8 88 [‌88‌]
eeeeeeee-8-eeee 88 [‌88‌]

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References


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