Synthesis of Stable Tri- and Tetra-Substituted [3]Dendralenes with an Allylsilane as Integral Component

A novel route to functionalized [3]dendralenes with an allylsilane as integral component has been developed. The key step involves a dimethylsulfonium methylide mediated olefination of appropriately substituted silylmethylethenylidene phosphonoacetate followed by Horner–Wadsworth–Emmons reaction with aromatic aldehydes. The tri- and tetra substituted [3]dendralenes are stable towards self Diels–Alder cyclodimerization which can be attributed to stereoelectronic effect of the silylmethyl group favoring for an unreactive conformation.