Synthesis of methyl (E)-4-[2-(2,3-dihydro-3-methyl-3-hydroxymethylbenzo[b]thien-5-yl)-1-propenyl]benzoate [(E)-3], methyl (E)-4-[2-(2,3-dihydro-3-methyl-3-hydroxymethyl-5-benzofuranyl)-1-propenyl]benzoate [(E)-4], and methyl(E)-4-[2-(2,3-dihydro-3,3-dimethyl-5-benzofuranyl)-3-hydroxy-1-propenyl]benzoate [(E)-7] as potential metabolites of selected heteroarotinoids with fused five-membered rings