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 δ-hydroxy-α,ß-unsaturated ketones having a benzylic hydroxyl group at the δ-position using allyltrimethylsilane mediated by BF3·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.

Total Synthesis and Structural Revision of Monocillin VII.

The first asymmetric total synthesis of macrolactone monocillin VII and its C-10' epimer was achieved starting from a known chiral pure epoxide in 16 longest linear sequences. The present synthesis highlights the macrolactone formation involving an alkyne-dicobalt carbonyl complex under De Brabander's conditions followed by an unexpected regioselective hydration. The asymmetric total synthesis resulted in the revision of the configuration at C10' and reassignment of the absolute configuration of the natural product.

A General Diastereoselective Strategy for Both cis- and trans-2,6-Disubstituted Tetrahydropyrans: Formal Total Synthesis of (+)-Muconin.

A protocol for general diastereoselective tandem dihydroxylation followed by SN2 cyclization was developed for the convenient and efficient synthesis of cis- and trans-2,6-disubstituted tetrahydropyrans from ζ-mesyloxy α,ß-unsaturated esters. The application of this novel method was demonstrated through the concise formal synthesis of (+)-muconin, a nonclassical acetogenin, with sequential THP-THF ring formation.