Highly stereoselective construction of the C2 stereocentre of α-tocopherol (vitamin E) by asymmetric addition of Grignard reagents to ketones?

Organic & Biomolecular Chemistry Pub Date: 2017-07-25 DOI: 10.1039/C7OB00751E

Abstract

Tertiary alcohol precursors of both C2 diastereoisomers of α-tocopherol were prepared in three ways by our recently reported asymmetric Grignard synthesis. The versatility of Grignard chemistry inherent in its three-way disconnection was exploited to allow the synthesis of three product grades: 77?:?23 dr (5 steps), 81?:?19 dr (5 steps) and 96?:?4 dr (7 steps, one gram scale) from readily available and abundant starting materials. The products were converted to their respective α-tocopherols in 3 steps, which allowed a definitive re-assignment of their absolute configurations.

Graphical abstract: Highly stereoselective construction of the C2 stereocentre of α-tocopherol (vitamin E) by asymmetric addition of Grignard reagents to ketones
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