An electrocyclization route to azetidine nitrones from N-alkenylnitrones was discovered that provides facile access to these unsaturated strained heterocycles. Reactivity studies showed that these compounds undergo a variety of reduction, cycloaddition, and nucleophilic addition reactions to form highly substituted azetidines with excellent diastereoselectivity. Taken together, these transformations provide a fundamentally different approach to azetidine synthesis than traditional cyclization by nucleophilic displacement and provide novel access to a variety of underexplored strained heterocyclic compounds.
A dearomative [3,3′]‐sigmatropic rearrangement that converts N‐alkenylbenzisoxazolines into spirocyclic pyrroline cyclohexadienones has been developed by using the dipolar cycloaddition of an N‐alkenylnitrone and an aryne to access these unusual transient rearrangement precursors. This cascade reaction affords spirocyclic pyrrolines that are inaccessible through dipolar cycloadditions of exocyclic cyclohexenones and provides a fundamentally new approach to novel spirocyclic pyrroline and pyrrolidine motifs that are common scaffolds in biologically‐active molecules. Diastereoselective functionalization processes have also been explored to demonstrate the divergent synthetic utility of the unsaturated spirocyclic products.
An asymmetric method for the synthesis of dihydropyrido[1,2-a]indoles from mixtures of nitrones and allenoates has been developed. This transformation showcases the use of squaramide catalysis in a complicated cascade system that has been shown to be highly sensitive to reaction conditions and substituent effects. The new method provides access to enantiomerically enriched dihydropyridoindoles from modular, non-indole reagents. The optimization and scope of the new transformation is discussed in addition to initial mechanistic experiments that indicate the role of the catalyst.
Lewis basic salts promote benzyltrimethylsilane
coupling with (hetero)aryl
nitriles, sulfones, and chlorides as a new route to 1,1-diarylalkanes.
This method combines the substrate modularity and selectivity characteristic
of cross-coupling with the practicality of a base-promoted protocol.
In addition, a Lewis base strategy enables a complementary scope to
existing methods, employs stable and easily prepared organosilanes,
and achieves selective arylation in the presence of acidic functional
groups. The utility of this method is demonstrated by the synthesis
of pharmaceutical analogues and its use in multicomponent reactions.
An electrocyclization route to azetidine nitrones from N-alkenylnitrones was discovered that provides facile access to these unsaturated strained heterocycles.R eactivity studies showed that these compounds undergo av ariety of reduction, cycloaddition, and nucleophilic addition reactions to form highly substituted azetidines with excellent diastereoselectivity.T aken together,t hese transformations provide af undamentally different approacht oa zetidines ynthesis than traditional cyclization by nucleophilic displacement and providen ovel access to av ariety of underexplored strained heterocyclic compounds. Scheme 2. Cycloaddition and reduction of azetidine nitrones. THF = tetrahydrofuran, Tf = trifluoromethanesulfonyl.
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