Stereoselective [2+2]-Cycloadditions of chiral allenic ketones and alkenes: Applications towards the synthesis of benzocyclobutenes and endiandric acids.

Cyclobutanes are important motifs that have found utility in many contexts. Prior work has demonstrated an enantioselective isomerization/stereoselective [2 + 2] as a means to access bicyclo [4.2.0] octanes. Herein, the utility of this method is demonstrated towards the synthesis of benzocyclobutenes and a key intermediate towards the endiandric acids.

Stereoselective [4+2]-Cycloaddition with Chiral Alkenylboranes.

A method for the stereoselective [4+2]-cycloaddition of alkenylboranes and dienes is presented. This transformation was accomplished through the introduction of a new strategy that involves the use of chiral N-protonated alkenyl oxazaborolidines as dieneophiles. The reaction leads to the formation of products that can be readily derivatized to more complex structural motifs through stereospecific transformations of the C-B bond such as oxidation and homologation. Detailed computation evaluation of the reaction has uncovered a surprising role of the counterion on stereoselectivity.

Evolution of a Strategy for the Enantioselective Synthesis of (-)-Cajanusine.

The first enantioselective synthesis of (-)-cajanusine is presented. Key features of the route include a rapid synthesis of the [4.2.0]bicyclooctane core by an enantioselective isomerization/stereoselective [2+2]-cycloaddition strategy as well as prominent use of catalytic methods for bond construction. The evolution of the approach is also presented that highlights unexpected roadblocks and how novel solutions were developed.

Synthesis of ent-[3]-Ladderanol: Development and Application of Intramolecular Chirality Transfer [2+2] Cycloadditions of Allenic Ketones and Alkenes.

An enantioselective synthesis of ent-[3]-ladderanol is presented. The ladderanes are an interesting class of molecules for their unique structure of fused cyclobutane rings as well as their perceived biological function of organism protection. The route hinges on the development and application of a chirality transfer [2+2] cycloaddition of an allenic ketone and alkene. Further stereocontrolled transformations allowed for completion of the synthesis. The scope of the chirality transfer [2+2] cycloaddition is also presented.