Conversion of alkynes into ketones by hydration is one of the most fundamental organic addition reactions. Traditional methods for alkyne hydration suffer from usage of toxic and costly metals, excessive acids, harsh conditions, and long reaction times, bringing about an urgent desire to explore more efficient and green protocols to complete this transformation. A metal-free efficient protocol for the accelerated hydration of alkynes in microdroplets was successfully developed in this work to overcome these drawbacks. The hydration process was finished under room temperature using only 18 mol % sulfuric acid as the catalyst and acetonitrile as the solvent. Complete conversions were feasible on the low millisecond time scale in microdroplets for a wide range of alkynes bearing functional groups, including electron-withdrawing groups and electron-donating groups. This is in sharp contrast to trace amounts of ketones or none in 20 min in bulk phase. Compared to the bulk reaction under the same conditions, the reactions in microdroplets are accelerated by 4 to 5 orders of magnitude as seen by the increase in measured rate constants. Further, the accelerated microdroplet hydration can be scaled up to an acetophenone amount of 57.2 ± 0.1 mg min −1 (3.43 ± 0.01 g h −1 ) by using 2 mol L −1 phenylacetylene sprayed at 300 μL min −1 . The microdroplet protocol offers several advantages including ultrahigh acceleration, complete conversion, mild reaction conditions (metal, light, and heat free), and minimal post purification, as well as a wide substrate scope, making it attractive for green and sustainable chemistry.

Epoxy compounds are an important class of organic intermediates that are generally used to synthesize many important compounds and natural products. Herein, we carried out two-phase epoxidation of α,β-unsaturated olefins in microdroplets without any catalysts, where all the yield measurements were made upon microdroplet collection using high performance liquid chromatography. The epoxidation reaction can only take place under thermal irradiation both in microdroplets and in bulk phase, and an optimal yield was obtained in microdroplets at a reaction temperature of 35 °C. The epoxidation yield in microdroplets (85%) was superior over that in bulk phase (13%). In addition, the microdroplet epoxidation also produced configuration-selective epoxy compounds

Because of their unique properties and high biological activities, organophosphorus compounds have been used worldwide in agricultural, industrial, medicinal, and veterinary applications. Conventional strategies for direct phosphonylation suffer from the usage of stoichiometric or excessive metallic or nonmetallic catalysts and long reaction times under harsh conditions, leading to a strong desire for environment-friendly protocols for phosphonylation. A protocol for the accelerated phosphonylation of N-phenyltetrahydroisoquinolines in minutes was developed without the use of any catalyst in microdroplets. The phosphonylation process was completed (>85% yields) in 10 min at 40 °C using 0.8 equiv 2,3-dicyano-5,6-dichlorobenzoquinone as the oxidant and acetonitrile as the solvent. The microdroplet phosphonylation strategy showed good suitability to alkyl phosphites and N-phenyltetrahydroisoquinolines bearing electron-withdrawing and electron-donating substitutes, and the yields of the microdroplet reaction were much greater than those of the bulk (accelerated by two orders of magnitude from the ratio of the rate constants using the microdroplet and the bulk method). Furthermore, microdroplet phosphonylation can be scaled up to a 1-phenyl-2-dimethylphosphonite-1,2,3,4-tetrahydroisoquinoline amount of 510 mg h–1 by spraying 0.1 mol L–1 N-phenyltetrahydroisoquinoline at 300 μL min–1. These figures of merit make it a promising alternative to classic organic methodologies for the synthesis of organophosphorus compounds.