Metal-Catalyzed Cyclization of β- and γ-Allenols Derived from D-Glyceraldehyde—Synthesis of Enantiopure Dihydropyrans and Tetrahydrooxepines: An Experimental and Theoretical Study
✍ Scribed by Benito Alcaide; Pedro Almendros; Teresa Martínez del Campo; Elena Soriano; José L. Marco-Contelles
- Publisher
- John Wiley and Sons
- Year
- 2009
- Tongue
- English
- Weight
- 499 KB
- Volume
- 15
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
Abstract
Regiocontrolled metal‐catalyzed preparations of enantiopure dihydropyrans and tetrahydrooxepines have been synthesized starting from β‐ and γ‐allenols derived from D‐glyceraldehyde. The Pd^II^‐catalyzed cyclizative coupling reactions of β‐allenols 1 a and 1 b with allyl bromide effectively afforded enantiopure tetrafunctionalized dihydropyrans through a 6‐endo oxycyclization protocol, whereas the gold‐, platinum‐, and palladium‐mediated heterocyclization of γ‐allenol 2 furnished tetrahydrooxepines 13–16 through regioselective 7‐__endo‐__trig oxycyclization reactions. Moreover, density functional calculations were performed to predict the regioselectivity of the γ‐allenol cycloetherification to tetrahydrooxepines on the basis of both the tether nature and characteristics of the metals, and to gain an insight into the mechanism of the oxycyclization reactions.