NOVELTY - Selective deoxygenation of hydroxybenzaldehydes, comprises: condensing syringaldehyde and functionalized phenylacetic acid with at least one first base and at least one anhydride; decarboxylating obtained aryl cinnamic acid with at least one decarboxylation catalyst at 30-200 degrees C or thermally at 100-350 degrees C to form first stilbene(s); hydrodeoxygenating stilbene(s) by converting to sulfonate(s) in presence of e.g. at least one second base in water; reducing obtained sulfonate(s) with reductive elimination catalyst to form second stilbene(s); and reacting second stilbene(s) with hydrolyzing agent.    USE - The method is useful for selective deoxygenation of hydroxybenzaldehydes to produce polyphenol i.e. trans-resveratrol or (E)-3,4',5-trimethoxy-4-hydroxystilbene (claimed), which is useful for: fabricating low-weight, composite aerospace structures; and producing thermoplastics or resins e.g. polysulfones, polyesters, polyester-styrene polymers, polycarbonates or epoxy resins.    ADVANTAGE - The method: utilizes the syringaldehyde, which is cheap and renewable phenol, and reduces the use of petroleum based feedstocks; is selective for the trans-isomer; performs the decarboxylation without using a copper catalyst; efficiently converts syringaldehyde into polyphenols; and is environmentally friendly.    DETAILED DESCRIPTION - Selective deoxygenation of hydroxybenzaldehydes, comprises: condensing syringaldehyde and a functionalized phenylacetic acid with at least one first base and at least one anhydride to produce an aryl cinnamic acid; decarboxylating the aryl cinnamic acid with at least one decarboxylation catalyst at 30-200 degrees C or thermally at 100-350 degrees C to produce first stilbene(s); hydrodeoxygenating the stilbene(s) by converting to sulfonate(s) in the presence of at least one second base in water or at least one organic solvent to obtain sulfonate(s); reducing the sulfonate(s) with a reductive elimination catalyst to produce a second stilbene(s); and reacting the second stilbene(s) with a hydrolyzing agent to generate a polyphenol.