ChemInform Abstract: Lewis Acid‐Promoted Condensation of Allylalkoxysilanes with Carbonyl Compounds. Synthesis of Tetrahydropyrans.

Abstract

ChemInform Abstract The allylalkoxysilane (I) reacts with the aldehydes (II) in the presence of aluminum trichloride to yield the cis-4-chloro-2,6-disubstituted tetrahydropyrans (III). When the reaction of the allylsilane (IV) with the aldehyde (V) is performed in the presence of boron trifluoride etherate, the homoallylic alcohol (VI) is produced. Ring closure reaction of the allylalkoxysilane (VII) with the aldehydes (IIa) -(IIc) in dichloromethane gives the 4-alkoxytetrahydropyrans (VIII). The 2,6-unsymmetrically substituted 4-chlorotetrahydropyrans (XIII) are prepared by conversion of dimethyldichlorosilane (IX) into the bisalkoxysilane (XII) and subsequent AlCl3-promoted cyclization with the aldehydes (II). Reaction of the allylalkoxysilane (XIV) with the aldehydes (XV) and (XVI) produces the (benzyloxyethyl)chloro(methyl)tetrahydropyran (XVII) which is dechlorinated, deprotected, and oxidized, giving the (methyltetrahydropyranyl)acetic acid (XIX) which is a secretion product of the civet cat.