Stereoselective nucleophilic substitution of 6-(tert-butyldimethylsilyloxy)-3,6-dihydro-2H-pyran-3-yl acetate: application to the synthesis of a NK1 receptor antagonist

Reaction of chiral cis- and trans-6-(tert-butyldimethylsilyloxy)-3,6-dihydro-2H-pyran-3-yl acetates with various nucleophiles (allyltrimethylsilane, bistrimethylsilylacetylene, benzyl alcohol, benzyl carbamate etc.) in the presence of a Lewis acid gave the corresponding 2,3-unsaturated pyran derivatives in good to excellent yield with trans selectivity. Application to the synthesis of NK1 antagonist is also described.