The stereoselective synthesis of tetrahydrofurans was achieved by formal [3+2]-cycloaddition of allyl and crotylsilanes with alpha-triethylsilyloxy aldehydes. The scope of the reaction was examined by using different alpha-substituted aldehydes and different substituents on the silicon. Tamao oxidation of the products resulted in formation of diols that are easily functionalized allowing an entry to natural products synthesis. The formal total synthesis of the muscarine alkaloids (-)-allomuscarine and (+)-epimuscarine was achieved.
The reaction of a series of beta-(triethylsilyloxy)aldehydes with several allylsilanes and crotyldimethylphenylsilane is described. Aldehydes possessing an alpha-stereocenter afforded tetrahydropyrans as mixtures of two diastereomers with allylsilane, but only a single diastereomer was observed in the case of crotylsilanes. The reaction time for crotylsilanes was longer than that for allylsilanes likely due to the increased steric hindrance. Allylsilanes afforded tetrahydropyrans in 34-67% yields, and crotylsilanes provided products in 0-62% yields.
Synthesis of Tetrahydrofurans from Protected β-Hydroxyaldehydes:Optimization of the Alcohol Protecting Group.-The conversion of silyl-protected β-hydroxyaldehydes (I) to tetrahydrofurans (III) by reaction with the diazoester (II) is investigated. Low yields of the desired tetrahydrofuran are obtained with aldehyde (Ic), while other protecting groups afford good to fair yields. -(ANGLE, S. R.; BERNIER, D. S.; EL-SAID, N. A.; JONES, D. E.; SHAW, S. Z.; Tetrahedron Lett. 39 (1998) 23, 3919-3922; Dep. Chem., Univ.
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