A catalyst-free oxyboration reaction of alkynes is developed. The resulting borylated isocoumarins and 2-pyrones are isolated as boronic acids, pinacolboronate esters, or potassium organotrifluoroborate salts, providing a variety of bench-stable organoboron building blocks for downstream functionalization. This method has functional group compatibility, is scalable, and proceeds with readily available materials: B-chlorocatecholborane and methyl esters. Mechanistic studies indicate that the B-chlorocatecholborane acts as a carbophilic Lewis acid toward the alkyne, providing a mechanistically distinct pathway for oxyboration that avoids B–O σ bond formation and enables this catalyst-free route.

This Review describes the development of strategies for carbonyl−olefin metathesis reactions relying on stepwise, stoichiometric, or catalytic approaches. A comprehensive overview of currently available methods is provided starting with Paterno−Buchi cycloadditions between carbonyls and alkenes, followed by fragmentation of the resulting oxetanes, metal alkylidene-mediated strategies, [3 + 2]-cycloaddition approaches with strained hydrazines as organocatalysts, Lewis acid-mediated and Lewis acidcatalyzed strategies relying on the formation of intermediate oxetanes, and protocols based on initial carbon−carbon bond formation between carbonyls and alkenes and subsequent Grob-fragmentations. The Review concludes with an overview of applications of these currently available methods for carbonyl−olefin metathesis in complex molecule synthesis. Over the past eight years, the field of carbonyl−olefin metathesis has grown significantly and expanded from stoichiometric reaction protocols to efficient catalytic strategies for ring-closing, ring-opening, and cross carbonyl− olefin metathesis. The aim of this Review is to capture the status quo of the field and is expected to contribute to further advancements in carbonyl−olefin metathesis in the coming years.9396 7.2. Cross Carbonyl−Olefin Metathesis 9396 8. Applications in Natural Product Synthesis 9398 9.

The first ring-forming thioboration reaction of C–C π bonds is reported. This catalyst-free method proceeds in the presence of a commercially available external electrophilic boron source (B-chlorocatecholborane) in good to high yields. The method is scalable and tolerates a variety of functional groups that are intolerant of other major borylation methods. The resulting borylated benzothiophenes participate in a variety of in situ derivatization reactions, showcasing that these borylated intermediates do not need to be isolated prior to downstream functionalization. This methodology has been extended to the synthesis of borylated dihydrothiophenes. Mechanistic experiments suggest that the operative mechanistic pathway is through boron-induced activation of the alkyne followed by electrophilic cyclization, as opposed to S–B σ bond formation, providing a mechanistically distinct pathway to the thioboration of C–C π bonds.

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We describe the development of a new catalyst system for carbonyl-olefin ring-closing metathesis reactions that relies on Lewis acidic superelectrophiles and significantly expands the current scope of this transformation to medium-sized rings. <div>Importantly, these superelectrophiles are shown to promote carbonyl-olefin metathesis via a distinct and unprecedented mechanism. </div>