BF3•OEt2-Catalyzed Unexpected Stereoselective Formation of 2,4-trans-Diallyl-2-methyl-6-aryltetrahydro-2H-pyrans with Quaternary Stereocenters

The present manuscript describes a convenient, mild, and highly stereoselective method for the allylation of delta-hydroxy-alpha,beta-unsaturated ketones having a benzylic hydroxyl group at the delta-position using allyltrimethylsilane mediated by BF3 center dot OEt2, leading to 2,4-diallyl-2-methyl-6-aryltetrahydro-2H-pyran ring systems with quaternary carbon stereogenic centers. This represents the first example of a tandem isomerization followed by one C-O and two C-C bond-forming reactions in one pot. The isolation of TMS-protected lactol as an intermediate from the reaction strongly supports the proposed mechanistic pathway.

Automated summary

This manuscript describes a convenient, mild, and highly stereoselective method for the allylation of delta-hydroxy-alpha,beta-unsaturated ketones using allyltrimethylsilane mediated by BF3 center dot OEt2, resulting in 2,4-diallyl-2-methyl-6-aryltetrahydro-2H-pyran ring systems with quaternary carbon stereogenic centers. The isolation of TMS-protected lactol as an intermediate strongly supports the proposed mechanistic pathway.