We report a Cu(II)-(S,S)-i Pr-FOXAP-catalyzed borylative Michael/Michael addition cascade cyclization of unsymmetrical dienone for the synthesis of highly substituted and functionalized all-carbon spiroindane boronates under mild conditions. A series of optically active spiroindanes bearing boronic ester were obtained with excellent yields and good to excellent enantioselectivities (≤97% ee) and diastereoselectivities (up to >20:1 dr). In addition, scale-up synthesis of this method and synthetic transformations of spiroindane boronates are also illustrated.
Disclosed here an amine‐catalyzed reductive aldol‐condensation followed by an intramolecular reductive Michael‐addition cascade employing Hantzsch ester as hydride source to a keto‐bis‐enone to provide enantio‐ and diastereoselective benzannulated diquinanes having three consecutive stereocenters, one of which is an all‐carbon quaternary formyl stereocenter. Interestingly, on changing a tether connecting the ketone and an enone moiety from an aliphatic to an aromatic, a change in reactivity is observed. In this case, instead of the above‐mentioned reductive aldol condensation, an asymmetric aldol reaction occurs, followed by an iminium/enamine isomerization and, finally diastereoselective Michael addition reaction occurs. As a result, a bis‐benzannulated diquinane is obtained with vicinal congested quaternary chiral centers.
An efficient cascade protocol for the stereoselective
synthesis
of borylated carbocycles via copper-catalyzed borylative Michael/Michael
cyclization is presented. Using this mild approach, up to 24 new boronic
ester substituted indanes, cyclohexanes, and cyclopentanes were prepared
in good yields with excellent diasteroselectivities and exceptional
functional group tolerance. Furthermore, carbacyclic boronates were
oxidized successfully through synthetic transformation. Gram-scale
synthesis of the present protocol was also carried out effectively.
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