Stereoselective Synthesis of Tetrahydrofurans via Formal [3+2]-Cycloaddition of Aldehydes and Allylsilanes. Formal Total Synthesis of the Muscarine Alkaloids (−)-Allomuscarine and (+)-Epimuscarine

The stereoselective synthesis of tetrahydrofurans was achieved by formal [3+2]-cycloaddition of allyl and crotylsilanes with α-triethylsilyloxy aldehydes. The scope of the reaction was examined by using different α-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.