Synthesis of Indoles via Palladium[0]-Mediated Ullmann Cross-Coupling of o-Halonitroarenes with α-Halo-enones or -enals

Abstract

[reaction: see text] Palladium[0]-mediated Ullmann cross-coupling of o-halonitrobenzene (1) and various related nitroarenes with a range of alpha-halo-enones (e.g., 2) or -enals readily affords the expected alpha-arylenones, e.g., 3, or -enals, which are converted into the corresponding indoles, e.g., 4, on reaction with dihydrogen in the presence of Pd on C.

Total Synthesis of Marinoquinoline A Using a Palladium(0)‐Catalyzed Ullmann Cross‐Coupling Reaction

“…The structure of 17 was determined by single-crystal X-ray analysis (see the Experimental Section). Exposure of ketone 17 to dihydrogen in the presence of 10 % Pd/C did not effect the hoped-for reductive cyclization reaction [8,14] in an efficient manner. Gratifyingly, however, treatment of the same substrate with magnesium metal in methanol [15] resulted in both the desired reductive cyclization reaction (without any attendant reduction of the resulting 3H-pyrroloA C H T U N G T R E N N U N G [2,3-c]quinolone core) and cleavage of the tosyl group.…”

“…The pivotal steps are a Pd 0 -catalyzed Ullmann cross-coupling of the 3-iodopyrrole-2-carboxaldehyde 13 with o-bromonitrobenzene (14), conversion of the resulting 3-arylpyrrole 15 into methylketone 17, and reductive cyclization of 17 by using magnesium in methanol to give target 1 in 85 % yield.…”

“…[12] Disappointingly, the predominant product of reaction (95 %) was 2,2'-dinitrobiphenyl, which arises from homocoupling of the nitroarene. Pleasingly, this process could be suppressed by using obromonitrobenzene (14) as the cross-coupling partner for pyrrole 13. Under the best conditions we have been able to identify thus far (see the Experimental Section) a 74 % yield of compound 15 was obtained.…”

Recent advancement of Ullmann-type coupling reactions in the formation of C–C bond

“…Moreover, Banwell and co-workers developed the synthesis of indoles (15.4) via Pd(0)-mediated Ullmann crosscoupling of o-halonitrobenzene (15.1) and with arrange of a-halo-enones (15.2) followed by reductive cyclization (Scheme 15) [54].…”

Synthesis of C-15 Vindoline Analogues by Palladium-Catalyzed Cross-Coupling Reactions

“…Among these, the Suzuki reaction is arguably the most robust, as was investigated first. The Suzuki coupling of 11 and phenyl boronic acid proceeded smoothly under standard conditions to give the expected biaryl (12) in 68% yield (Scheme 2). We next examined the Heck reaction of 11 with a number of coupling partners.…”