The present invention relates to 6, 6a-dihydrofuro[3, 2-b]furan-2-(5H)one derivatives having a formula of structure (A) wherein R1, R2, R3, R4, R5 and R6 are defined as set forth in the description, and to pharmaceutically acceptable salts thereof, for use in medicine, in particular as antitumour compounds.The invention also relates to a process for preparing the aforesaid compounds which comprises a double cyclisation reaction of 4-in-1, 3-diol organic substrates with the incorporation of a molecule of carbon monoxide, catalysed by a palladium halide in the presence of potassium iodide.Furthermore, the invention is aimed at 6, 6a-dihydrofuro[3, 2-b]furan-2-(5H)one derivatives having a formula of structure (A), wherein R1, R2, R3, R4, R5 and R6 are defined as set forth in the description, wherein, when R1 is methyl or hydrogen, R2 is selected from the group consisting of alkyl, aryl and heteroaryl.