Science of Synthesis

Joule, J. A., Science of Synthesis, (2001) 10, 426.

A Leimgruber–Batcho-type intermediate is almost certainly involved in a sequence (‌Scheme 103‌) which begins with the ready base-catalyzed condensation of an o-nitroaraldehyde ‌367‌ with nitromethane to give a 1-nitro-2-(o-nitroaryl)ethene ‌368‌. Commonly, sodium hydroxide or ammonium acetate/acetic acid are used to promote the condensation; potassium fluoride is also used.[‌258‌] The 1-nitro-2-(o-nitroaryl)ethenes can also be obtained by nitration of 1-aryl-2-nitroethenes.[‌259‌,‌260‌] Reduction, traditionally with metal/acid combinations,[‌259‌–‌262‌] then leads to a 2,3-unsubstituted indole ‌372‌, the simplest interpretation for which being the formation of an intermediate arylamino-enamine ‌369‌ (not isolated) comparable to that involved in the Leimgruber–Batcho sequence. As in that sequence, protonation of ‌369‌ gives ‌370‌, heterocyclic ring closure to ‌371‌ being followed by final loss of ammonia producing the indole ‌372‌. Alternative methods for the reductive cyclization of 1-nitro-2-(o-nitroaryl)ethenes include (see ‌Table 6‌): catalytic transfer hydrogenation,[‌263‌] titanium(III) chloride,[‌264‌] sodium borohydride/palladium/carbon,[‌265‌] hydrogen/palladium(II) hydroxide/carbon,[‌266‌] palladium/carbon/ammonium formate/formic acid,[‌263‌] and iron/acetic acid/silica gel.[‌260‌]

‌Meeeee 888‌ Meeeeee eeee 8-Meeee-8-(e-eeeeeeeee)eeeeeee

‌Meeee 8‌ Meeeeee eeee 8-Meeee-8-(e-eeeeeeeee)eeeeeee

Meeeeeee Meeeeeee	Meeeeeee Meeeeeeeee M	Meeeeeee Meeeeeeeee MM	Meeeeee	Meeee (%)	Mee
8-[8,8-eee(eeeeeeeee)eeeeee]-8-eeeeeeeeeee	eeeee MMM8, MeMM	Me, MeMM, eeeeee		88	[‌888‌]
8-eeeeee-8-eeeeeeeeeeeeeeeee	MeMM8, MeMM, MeMM, −88°M eeee Me8M, eeeeee	M8, Me/M, MeMMe, MeMM		88	[‌888‌]
8,8-eeeeeeeee-8-eeeeeeeeeeeeeeeee	MeMM8, MM8MMe, MeMM, 88°M	M8 (88.8 eee), Me(MM)8/M, MMM, MeMM, 88°M		88	[‌888‌]
8-(8,8-eeeeeeeee-8-eeeeeeeeeee)-8-eeeeeeeeeee		Me/M, MM8MMM8, MeMM, eeeeee, M8		88	[‌888‌]
8-(8-eeeeeeeee-8-eeeeeee-8-eeeeeeeeeee)-8-eeeeeeeeeee		Me, MeMM, eeeeee eee, eeeeeee/eeeeeeeeeee (8:8), eeeeee		88	[‌888‌]

Meeeeeeeeeee Meeeeeeee

8,8-Meeeeeeee-8M-eeeeee; Meeeeee Meeeeeeee:[‌888‌]

8,8-Meeeeeeee-8-eeeeeeeeeeeeeeeee (88.8 e, 888 eeee) eee eeeeeeeee eeee MeMM8 (88 eM) eeeee MM8MMe (88.8 e, 888 eeee) ee MeMM (88 eM) ee 88°M eee 8 e. Meeeeeee ee eMeMM (888 eM) eeee eeeeeee eee 8.8 e eee eeeeeee ee ee eeee 8-(8,8-eeeeeeeee-8-eeeeeeeeeee)-8-eeeeeeeeeee; eeeee: 88.8 e (88%); ee 888–888°M.

8-(8,8-Meeeeeeee-8-eeeeeeeeeee)-8-eeeeeeeeeee (88.8 e,888 eeee) eee eeeeeee eeee M8 ee 88.8 eee eee ee 88°M eeee 88% Me(MM)8/M (88 e) eee 8.8 e. Mee eeeeeee eee eeeeee, e eeeeeee eeeeeeee ee eeeeeeee (8 e) eeeee eee eee eeeeeeeeeeeee eeeeeeeee ee eeeeee eee e eeeeeee 8 e. Mee eeeeee eeeeeee eee eeeeeeee eeeeeee Meeeee eee eeeeeeeeeeee eeeeeeeee ee eee eeeee eee eeeeeeeee ee MM8Me8, eeeeee eeee M8M eeee ee MeMMM8, eeeee (MeMM8) eee eeeeeeee (eeeeee eee, MM8Me8) ee eeee eeeeeeee eeeee, ee eeeeeeeeeee eeee eMeMM eeee eee eeeeeee; eeeee: 88 e (88%); ee 888–888°M.

References