Polymerization of 3,4-ethylenedioxythiophene (EDOT) produces the conductive polymer PEDOT, an organic electronic material that possesses inherent stability, low oxidation potential, high conductivity and excellent electrochromic properties. Attachment of a functional group onto the dioxinyl ring moiety can serve as a reactive site to introduce a variety of substituents onto the polymer backbone. These substituents may influence the optical and electrochemical properties of PEDOT. This report details the synthesis of O-substituted derivatives of the well characterized hydroxymethyl derivative of EDOT, EDTM (2,3-dihydrothieno[3,4-b]-1,4-dioxin-2-yl methanol), principally of the compound EDTM-6-hexanoic acid; and an improved synthesis of the parent compound EDTM. Improvements of the synthesis of EDTM include employing the Zaugg procedure to produce sodium ethoxide for the Hinsberg thiophene synthesis; and separation of the desired EDTM diester product thienodioxine ring isomer from the by-product thienodioxepine diester ring isomer formed during the fused ring formation reaction. Reaction of diethyl 3,4-dihydroxythiophene-2,5-dicarboxylate with epibromohydrin in ethanolic aqueous potassium carbonate affords the two products, the major desired EDTM diester and the by-product dioxepine diester, in a 5:2 ratio.