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

Abstract

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.

Efficient Chirality Transfer in the SmI2-Mediated Cyclization of Aldehydo β-Alkoxyvinyl Sulfoxides: Asymmetric Synthesis of 3-Hydroxyoxanes

“…The oxacyclic products obtained in the present studies may serve as precursors in further transformations. For example, sodium amalgam reduction of the sulfone functional group in 31 and reductive debenzylation by Raney nickel afforded the known diol 34 , which constitutes a formal synthesis of (+)-epimuscarine ( 35 ) 12 (Scheme 8).

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Muscarine, imidazole, oxazole, and thiazole alkaloids

“…A stereoselective synthesis of tetrahydrofurans has been achieved by formal [3 ϩ 2]-cycloaddition of allyl and crotylsilanes with α-triethylsilyloxy aldehydes. 4 The methodology provided a concise pathway for the synthesis of (Ϫ)-allomuscarine 2 and (ϩ)-epi-muscarine 3.…”

Access to stereodefined (Z)-allylsilanes and (Z)-allylic alcohols via cobalt-catalyzed regioselective hydrosilylation of allenes

“…Allylsilanes are synthetically valuable building blocks because of their non-toxicity, high stability and versatile applications in organic synthesis and material science 1 – 3 . They have been employed as monomers for syntheses of silicon-containing polymers and undergo a variety of organic transformations 4 – 6 . As such, various methods have been developed to prepare allylsilanes and the majority of these approaches produce thermodynamically more stable ( E )-allylsilanes 7 – 9 .…”