Highly Diastereoselective Chelation-Controlled 1,3-anti-Allylation of (S)-3-(Methoxymethyl)hexanal Enabled by Hydrate of Scandium Triflate

En route to the total synthesis of (+)-Neopeltolide, we explored Lewis acid-assisted diastereoselective allylation MOM-protected 3-hydroxylhexanal with β-(2,2-diethoxyethyl)-substituted (allyl)tributylstannane. The hydrated form scandium triflate was found be essential for attaining high 1,3-anti-diastereoselectivity (d.r. 94:6), while use anhydrous catalyst resulted in a modest diastereocontrol 76:24). preferred 1,3-anti-selectivity this transformation can rationalized framework Reetz chelate model asymmetric induction. 1,3-anti-configuration product confirmed by its conversion into known C7-C16 building block (+)-Neopeltolide. We also report an improved protocol (allyl)tributylstannane, which utilized as cost-efficient bipolar isoprenoid-type C5-building natural compounds.