79% |
With (1,5-cyclooctadiene)(methoxy)iridium(I) dimer; 4,4'-di-tert-butyl-2,2'-bipyridine In tert-butyl methyl ether at 80℃; for 0.333333h; Inert atmosphere; Microwave irradiation; Sealed tube; |
|
76% |
Stage #1: bis(pinacol)diborane With (1,5-cyclooctadiene)(methoxy)iridium(I) dimer; 4,4'-di-tert-butyl-2,2'-bipyridine In tert-butyl methyl ether Inert atmosphere; Sonication;
Stage #2: methyl 1-(tert-butyloxycarbonyl)pyrrole-2-carboxylate at 80℃; for 0.333333h; Inert atmosphere; Microwave irradiation; |
1 1 -tert-Butyl 2-methyl 4-(4,4,5 ,5 -tetramethyl- 1,3 ,2-dioxaborolan-2-yl)- 1 H-pyrrole- 1,2- dicarboxylate
4,4,4’,4’,5 ,5 ,5 ‘,5’-Octamethyl-2,2’-bi(1 ,3 ,2-dioxaborolane) (59.2 g, 233.08 mmol), (1,5- cyclooctadiene)(methoxy) iridium (I) dimer (1 .177 g, 1.78 mmol) and 4,4’-di-tert-butyl- 2,2’-bipyridine (0.953 g, 3.55 mmol) were placed in a 500 mL three-necked flask, which was purged with nitrogen. Degassed MTBE (500 mL) was added and the mixture was stirred and sonicated until a clear brown solution was obtained. 1-tert-butyl 2-methyl 1H-pyrrole-1,2-dicarboxylate (Sigma Aldrich) (50 g, 221.98 mmol) was added and flushed with nitrogen. The solution was heated in a microwave reactor at 80 °C for 20 minutes. The mixtures were combined and evaporated. The crude product was purified by flash silica chromatography, elution gradient 50 to 100% DCM in heptane to afford 1 -tert-butyl 2-methyl 4-(4,4,5 ,5 -tetramethyl- 1,3 ,2-dioxaborolan-2-yl)- 1 H-pyrrole- 1 ,2-dicarboxylate(59.3g, 76%) as a white crystalline solid. |
68% |
With (1,5-cyclooctadiene)(methoxy)iridium(I) dimer; 4,4'-di-tert-butyl-2,2'-bipyridine In tert-butyl methyl ether at 65℃; for 2h; |
1-tert-Butyl 2-Methyl 4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrrole-1,2-dicarboxylate (1e)23
Bis(pinacolato)diboron (10.65 g, 41.96 mmol), (1,5-cyclooctadiene)(methoxy)iridium(I) dimer (0.424 g, 0.64 mmol) and 4,4′-di-tertbutyl-2,2′-bipyridine (BBBPY, 0.354 g, 1.32 mmol) were placed in a250 mL three-necked flask, which was purged with N2. Degassed tertbutylmethyl ether (MTBE) (100 mL) was added and the mixture wasstirred until a clear brown solution was obtained. 1-tert-Butyl 2-methyl 1H-pyrrole-1,2-dicarboxylate24 (9.00 g, 39.96 mmol) was addedand the mixture stirred at 65 °C for 2 h. The reaction was cooled toRT and concentrated in vacuo. The crude product was purified byflash silica gel chromatography with DCM as eluent. Fractions wereevaporated to afford a liquid. Heptane (60 mL) was added and thesolution was left stirring overnight. The resultant precipitate was filteredand washed with 5% DCM in heptane; yield: 9.60 g (68%); offwhitesolid (Lit.23 mp 133-135 °C).1H NMR (500 MHz, CDCl3): = 1.31 (s, 12 H), 1.58 (s, 9 H), 3.82 (s, 3H), 7.12 (d, J = 1.7 Hz, 1 H), 7.68 (d, J = 1.7 Hz, 1 H).MS (ES+): m/z = 297 ([M + H]+ - OtBu). |