Diastereo- and Enantioselective Synthesis of Functionalized Dihydropyrans via an Organocatalytic Claisen Rearrangement/Oxa-Michael Addition Tandem Sequence

A straightforwarddiastereo- and enantioselective Claisen rearrangement/oxa-Michaeladdition tandem sequence with a cinchona squaramide catalyst was described,which afforded a practical and atom-economical approach to accessa range of valuable dihydropyrans in good to excellent yields withexcellent stereoselectivities. The organo-bifunctional catalyst playeda key role in enhancing stereoselectivity in this asymmetric tandemsequence. Moreover, the asymmetric catalytic sequential processesof the hydroalkoxylation/Claisen rearrangement/cyclization sequenceand Claisen rearrangement/aza-Michael addition tandem sequence havealso been afforded good yields and moderate stereoselectivities.

Automated summary

A straightforward diastereo- and enantioselective Claisen rearrangement/oxa-Michael addition tandem sequence with a cinchona squaramide catalyst was developed for the synthesis of valuable dihydropyrans. The organo-bifunctional catalyst played a crucial role in enhancing the stereoselectivity in this asymmetric tandem sequence. Additionally, good yields and moderate stereoselectivities were achieved in the asymmetric catalytic sequential processes of hydroalkoxylation/Claisen rearrangement/cyclization and Claisen rearrangement/aza-Michael addition tandem sequences.