Diels-Alder ring-opening process

A process for the ring-opening of a cycloadduct comprising a cylcoadduct according to formula I,

• wherein R1 and/or R2 are independently selected from the group consisting of H, C1-C20 alkyl, CHO and hydrazones, oximes, hemiacetals and acetals thereof, CH2OH and esters and ethers thereof, CO2H and esters thereof, and amides and tertiary amines of CH2NH2 and optionally polymer supported;
• R3 and/or R4 are independently selected from the group consisting of CH3, acetals, hemiacetal, hydrazones and oximes of CHO, CH2OH and esters and ethers thereof, CO2H and esters thereof, amides and tertiary amines of CH2NH2, and an electron withdrawing group that is selected from the group consisting of H, CF3, CCl3, CBr3, CI3, NO2, CN, SO2Q, SO3Q, COQ, COF, COCl, COBr, COI, C(O)Q, CO2Q, C(O)NQ, and C(═NT)Q, wherein Q and T are independently H, or linear or branched C1-C8-alkyl, optionally substituted with halogens and optionally polymer supported,
• or R3 and R4 together represent —(CO)X(CO)—, wherein X═O, CH2, NH, NMe, NEt, NPr, NBu, NPh, or S;
• or R2 and R4 together represent —CH2ZC(O)—, wherein Z is selected from the group consisting of O, NH and S;
• wherein represent a single or double bond;
• wherein said process comprises contacting the cycloadduct with an acidic mixture comprising sulfuric acid and an activating agent to obtain a ring-opened product;
• and
• wherein the molar ratio of sulfuric acid to cycloadduct is 2:1 to 0.01:1.