Selective Synthesis of alpha-Alkoxy Enones by alpha-Addition of Alcohols to Alkynones Using 1,1,1,3,3,3-Hexafluoroisopropanol and PPh3 as Co-catalysts

alpha-Alkoxy enones are quite useful building blocks in organic chemistry. The existing methods for syntheses of these compounds remain somewhat limited. Over the past years, nucleophilic phosphine catalysis has emerged as a practical and powerful tool for constructing diverse molecules with the advantages of environmental-friendly, metal-free, and mild reaction conditions. Meanwhile, alkynone is easy to prepare, can undergo a variety of reactions, and is a commonly used substrate for organic synthesis. alpha-Addition of alcohols to alkynones is a direct way to construct alpha-alkoxy enones. In this study, it was delightful to find that using PPh3 (10 mmol %) and 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) (20 mmol %) could redirect from beta-addition to alpha-addition. With this approach, a variety of alpha-alkoxy enones could be obtained directly with good yields and regioselectivity. Under optimal conditions, the generality of the reaction was investigated. Substrate scope studies showed that the reaction was well tolerated with many alcohols. Mechanistic study is also demonstrated.