Enantioselective Synthesis of Multifunctionalized 4H-Pyrans via Formal [4 + 2] Annulation Process by Bifunctional
Jia-Hong Wu1, Jianke Pan1, Juan Du1
1Key Laboratory of Green Chemistry & Technology of Ministry of Education, College of Chemistry , Sichuan University , Chengdu 610064 , P. R. China.
Abstract:
A highly enantioselective formal [4 + 2] annulation involving electron-deficient allenes as C2-synthons has been developed under bifunctional phosphonium salt catalysis. With this catalytic protocol, a wide range of synthetically interesting and highly functionalized chiral 4H-pyran derivatives were readily prepared in good yields (up to 99%) with outstanding diastereo- and enantioselectivities (up to >20:1 dr, up to >99.9% ee). The utility and the practicality of this method were demonstrated by the gram-scale reaction and facile elaboration. Of note, this is the first example of an asymmetric annulation reaction involving allenic reactants under a phase-transfer catalysis system.
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