Flow Chemistry

Timothy F. Jamison at MIT developed (Org. Lett. 2013, 15, 710. DOI: 10.1021/ol400051n) a metal-free continuous flow hydrogenation of alkene 1 using the protected hydroxylamine reagent 2 in the presence of free hydroxylamine. The reduction of nitroindole 4 to the corresponding aniline 5 using in situ-generated iron oxide nanocrystals in continuous flow was reported (Angew. Chem. Int. Ed. 2012, 51, 10190. DOI: 10.1002/anie.201205792) by C. Oliver Kappe at the University of Graz. A flow method for the MPV reduction of ketone 6 to alcohol 7 was disclosed (Org. Lett. 2013, 15, 2278. DOI: 10.1021/ol400856g) by Steven V. Ley at the University of Cambridge. Corey R. J. Stephenson, now at the University of Michigan, developed (Chem. Commun. 2013, 49, 4352. DOI: 10.1039/C2CC37206A) a flow deoxygenation of alcohol 8 to yield 9 using visible light photoredox catalysis.

Stephen L. Buchwald at MIT demonstrated (J. Am. Chem. Soc. 2012, 134, 12466. DOI: 10.1021/ja305660a) that arylated acetaldehyde 11 could be generated from aminopyridine 10 by diazonium formation and subsequent Meerwein arylation of ethyl vinyl ether in flow. The team of Takahide Fukuyama and Ilhyong Ryu at Osaka Prefecture University showed (Org. Lett. 2013, 15, 2794. DOI: 10.1021/ol401092a) that p-iodoanisole (12) could be converted to amide 13 via low pressure aminocarbonylation using carbon monoxide generated from mixing formic and sulfuric acids.

The continuous flow Sonogashira coupling of alkyne 14 to produce 15 using a Pd-Cu dual reactor was developed (Org. Lett. 2013, 15, 65. DOI: 10.1021/ol303046e) by Chi-Lik Ken Lee at Singapore Polytechnic. A tandem Sonogashira/cycloisomerization procedure to convert bromopyridine 16 to aminoindolizine 18 in flow was realized (Adv. Synth. Catal. 2012, 354, 2373. DOI: 10.1002/adsc.201200316) by Keith James at Scripps, La Jolla.

A procedure for the Pauson-Khand reaction of alkene 19 to produce the bicycle 20 in a photochemical microreactor was reported (Org. Lett. 2013, 15, 2398. DOI: 10.1021/ol4008519) by Jun-ichi Yoshida at Kyoto University. Kevin I. Booker-Milburn at the University of Bristol discovered (Angew. Chem. Int. Ed. 2013, 52, 1499. DOI: 10.1002/anie.201208892) that irradiation of N-butenylpyrrole 21 in flow produced the rearranged tricycle 22.

Professor Jamison described (Angew. Chem. Int. Ed. 2013, 52, 4251. DOI: 10.1002/anie.201300504) a unique peptide coupling involving the photochemical rearrangement of nitrone 23 to the hindered dipeptide 24 in continuous flow. Dong-Pyo Kim at Pohang University of Science and Technology developed (Angew. Chem. Int. Ed. 2013, 52, 6735. DOI: 10.1002/anie.201301124) a nanobrush microreactor with immobilized OsO₄ that achieves efficient dihydroxylation of alkene 25 with low loadings of the toxic metal.

Lastly, Prof. Buchwald developed (Angew. Chem. Int. Ed. 2013, 52, 3434. DOI: 10.1002/anie.201208544) a mild flow method for the cross-coupling of aryl chloride 27 with hydrazine to produce the aryl hydrazine 28. Subsequent engagement of 28 in a Fischer indole synthesis with ketone 29 under batch conditions furnished the indole 30 in high yield over the two steps.