Compounds of the formula I in which R 1 denotes A or Cyc, R 2 denotes H, F, Cl, Br, OH, CN, NO 2, A', OA', SA', SO 2 Me, COA' or CONA' 2, R denotes Ar or Het, X 1, X 2, X 3, X 4 each, independently of one another, denote CH or N, A denotes unbranched or branched alkyl with 1-10 C-atoms, wherein two adjacent carbon atoms may form a double bond and/or one or two non-adjacent CH- and/or CH 2 -groups may be replaced by N-, O- and/or S-atoms and wherein 1-7 H-atoms may be replaced by R 4, Cyc denotes cycloalkyl with 3-7 C-atoms, which is unsubstituted or monosubstituted by OH, Hal or A, A' denotes unbranched or branched alkyl with 1-6 C-atoms, wherein 1-5 H-atoms may be replaced by F, R 4 denotes F, Cl, Br, OH, CN, NO 2, A', OA', SA', SO 2 Me, COA' or CONA' 2, Ar denotes phenyl, which is unsubstituted, or mono-, di-, tri-, tetra- or pentasubstituted by Hal, A, [C(R 3) 2] p OR 3, [C(R 3) 2] p N(R 3) 2, NO 2, CN, [C(R 3) 2] p COOR 3, N(R 3) 2 COA, NR 3 SO 2 A, [C(R 3) 2] p SO 2 N(R 3) 2, S n A, O[C(R 3) 2] m N(R 3) 2, NHCOOA, NHCON(R 3) 2 and/or COA, R 3 denotes H or unbranched or branched alkyl with 1-6 C-atoms, Het denotes a mono- or bicyclic saturated, unsaturated or aromatic heterocycle having 1 to 4 N, O and/or S atoms, which may be unsubstituted or mono-, di-, tri-, tetra- or pentasubstituted by Hal, A, [C(R 3) 2] n OR 3, [C(R 3) 2] n N(R 3) 2, SR 3, NO 2, CN, COOR 3, CON(R 3) 2, NR 3 COA, NR 3 SO 2 A, SO 2 N(R 3) 2, S m A, O[C(R 3) 2] n N(R 3) 2, NHCOOA, NHCON(R 3) 2, CHO, COA, =S, =NH, =NA and/or =O (carbonyl oxygen), Hal denotes F, Cl, Br or I, n1, n2, n3, n4 denote 1, m denotes 1, 2 or 3, n denotes 0, 1 or 2, p denotes 0, 1, 2, 3 or 4, with the proviso that only one or two of X 1, X 2, X 3, X 4 denote N, and pharmaceutically acceptable salts, tautomers and stereoisomers thereof, including mixtures thereof in all ratios, excluding the compounds tert-butyl 2-[2-[ -2-ethoxycarbonylpyrrolidin-1-yl]-4,6-dimethyl-pyrimidine-5-carbonyl]-1,3,3a,4,6,6a-hexahydropyrrolo[3,4-c]pyrrole-5-carboxylate, tert-butyl 2-[2-(1,1-dioxo-1,2-thiazolidin-2-yl)-4,6-dimethyl-pyrimidine-5-carbonyl]-1,3,3a,4,6,6a-hexahydropyrrolo[3,4-c]pyrrole-5-carboxylate, tert-butyl 2-[2-[4-(methanesulfonamido)-1-piperidyl]-4,6-dimethyl-pyrimidine-5-carbonyl]-1,3,3a,4,6,6a-hexahydropyrrolo[3,4-c]pyrrole-5-carboxylate. R 1 denotes A or Cyc, R 2 denotes H, F, Cl, Br, OH, CN, NO 2, A', OA', SA', SO 2 Me, COA' or CONA' 2, R denotes Ar or Het, X 1, X 2, X 3, X 4 each, independently of one another, denote CH or N, A denotes unbranched or branched alkyl with 1-10 C-atoms, wherein two adjacent carbon atoms may form a double bond and/or one or two non-adjacent CH- and/or CH 2 -groups may be replaced by N-, O- and/or S-atoms and wherein 1-7 H-atoms may be replaced by R 4, Cyc denotes cycloalkyl with 3-7 C-atoms, which is unsubstituted or monosubstituted by OH, Hal or A, A' denotes unbranched or branched alkyl with 1-6 C-atoms, wherein 1-5 H-atoms may be replaced by F, R 4 denotes F, Cl, Br, OH, CN, NO 2, A', OA', SA', SO 2 Me, COA' or CONA' 2, Ar denotes phenyl, which is unsubstituted, or mono-, di-, tri-, tetra- or pentasubstituted by Hal, A, [C(R 3) 2] p OR 3, [C(R 3) 2] p N(R 3) 2, NO 2, CN, [C(R 3) 2] p COOR 3, N(R 3) 2 COA, NR 3 SO 2 A, [C(R 3) 2] p SO 2 N(R 3) 2, S n A, O[C(R 3) 2] m N(R 3) 2, NHCOOA, NHCON(R 3) 2 and/or COA, R 3 denotes H or unbranched or branched alkyl with 1-6 C-atoms, Het denotes a mono- or bicyclic saturated, unsaturated or aromatic heterocycle having 1 to 4 N, O and/or S atoms, which may be unsubstituted or mono-, di-, tri-, tetra- or pentasubstituted by Hal, A, [C(R 3) 2] n OR 3, [C(R 3) 2] n N(R 3) 2, SR 3, NO 2, CN, COOR 3, CON(R 3) 2, NR 3 COA, NR 3 SO 2 A, SO 2 N(R 3) 2, S m A, O[C(R 3) 2] n N(R 3) 2, NHCOOA, NHCON(R 3) 2, CHO, COA, =S, =NH, =NA and/or =O (carbonyl oxygen), Hal denotes F, Cl, Br or I, n1, n2, n3, n4 denote 1, m denotes 1, 2 or 3, n denotes 0, 1 or 2, p denotes 0, 1, 2, 3 or 4,