Exploring the Synthetic Application of Allylic Alcohol Isomerization

Allylic alcohol transposition lacks a thermodynamic driving force and usually displays stereoinfidelity and poor regioselectivity. However, regio- and stereoselectivity can be achived by coupling allylic alcohol transposition to a subsequent step that is kinetically and thermodynamically favorable. Based on this rationale, the allylic alcohol transposition and capture sequence was delevoped and applied successfully in heterocycle synthesis. Regio- and stereoselectivity were achieved when a pre-existing stereogenic center in the substrates could induce significant thermodynamic difference between diastereomeric products and when the individual steps toward these diastereomeric products were reversible.;Epoxides were later used as ennantioenriched electrophiles in this transposition/trapping sequence for stereoselective synthesis of heterocycles. The mechanism for this transformation was elucidated and a cascade approach using epoxides as trapping agents in the transposition of allylic alcohols was developed and applied in the stereoselective formation of polycyclic ethers.;Finally, an improved sequence using "traceless trapping agents" was developed. This new method did not leave any vestige in the resulting product and offered much more freedom for the application of allylic alcohol transposition in heterocycle synthesis. Understanding the relative rates of the steps in this new sequence led to the design of reactions that created multiple stereogenic centers with good to excellent levels of control.