Click Chemistry Under Microwave or Ultrasound Irradiation

Abstract

The copper-catalyzed azide-alkyne cycloaddition (CuAAC) is generally recognized as the most striking example of "click reaction". CuAAC fit so well into Sharpless' definition that it became almost synonymous with "click chemistry" itself. The most common catalyst systems employ Cu(II) salt in the presence of a reducing agent (i.e. sodium ascorbate) to generate the required Cu(I) catalyst in situ or as an alternative the comproportionation of Cu(II)/Cu(0) species. Although, Cu(I) catalyzes the reaction with a rate enhancement of 10 7 even in the absence of ligands and provides a clean and selective conversion to the 1,4-substituted triazoles, some bulky and scantily reactive substrates still require long reaction times and often few side products are formed. Outstanding results have been achieved by performing CuAAC under microwave (MW) irradiation. Several authors described excellent yields, high purity and short reaction times. In few cases also power ultrasound (US) accelerated the reaction, especially when heterogeneous catalysts or metallic copper are employed. The aim of this review is to summarize and highlight the huge advantages offered by MW-and US-promoted CuAAC. In the growing scenario of innovative synthetic strategies, we intend to emphasize the complementary role played by these non-conventional energy sources and click chemistry to achieve process intensification in organic synthesis.

A Fluorous Proline Organocatalyst with Acetone‐Dependent Aldolase Behavior

“…Propargylation of commercially available polyfluorododecanol led to ether 4 . Then, a CuAAC reaction of proline derivative 5 14 with polyfluoro ether 4 , performed under microwave conditions,15 allowed the easy and highly reproducible synthesis of triazole 6 . Finally, sequential cleavage of the methyl ester and the N ‐ tert ‐butoxycarbonyl (Boc) group led to target fluorous triazolylproline 7 .…”

Enabling technologies built on a sonochemical platform: Challenges and opportunities

“…The reaction does not require ligands and reducing agents, and can be applied to sensitive and highly functionalized molecules like cyclodextrins (Scheme 2). In general, this one-pot protocol affords products in higher yields (> 80 percent) and in much shorter times than conventional heating does (6-10 h) [20]. In materials chemistry, a few reports have documented the favourable combination of US and MW for the preparation of nanomaterials [21].…”

Effects of Ultrasound and Microwaves on Selective Reduction: Catalyst Preparation and Reactions

“…It offers the potential for shorter reaction cycles, cheaper reagents, and milder reaction conditions. [13,16,[89][90][91][92] The advantages of US in chemical reactions could be applied in industrial application in pharmaceutical or fine chemical industry. Sonochemistry can be used for fast reactions or in the synthesis of expensive products.…”