The expanding utility of continuous flow hydrogenation

Area of Science:

• Organic Chemistry
• Chemical Engineering
• Synthetic Chemistry

Background:

• Flow hydrogenation is increasingly recognized for improving reduction reactions.
• Flow reactors offer enhanced laboratory safety by containing pyrophoric catalysts and generating hydrogen in situ.
• This review examines recent advancements in applying flow chemistry to various reduction processes.

Purpose of the Study:

• To review recent applications of flow chemistry in hydrogenation for diverse synthetic reductions.
• To highlight methodologies for chemoselective and enantioselective reductions using flow hydrogenation.
• To demonstrate the advantages of flow hydrogenation, including improved yields and safety.

Main Methods:

• Review of literature on flow chemistry applied to hydrogenation.
• Examination of reductions involving nitro, imine, nitrile, amide, azide, and azo compounds.
• Analysis of de-aromatisation, hydrodehalogenation, and reductions of olefins, alkynes, carbonyls, and benzyl groups.

Main Results:

• Flow hydrogenation demonstrates broad applicability across numerous synthetic transformations.
• Enhanced reaction throughput, yields, and simplified workup are key benefits.
• Chemoselective and enantioselective reduction protocols have been successfully developed.

Conclusions:

• Flow hydrogenation offers significant advantages over batch processes for reduction reactions.
• The use of flow reactors enhances safety and efficiency in chemical synthesis.
• Flow chemistry is well-suited for multistep and cascade synthetic protocols.