1 2, 4-Triazoline-3,5-Diones

Synthesis, C-H bond functionalisation and cycloadditions of 6-styryl-1,2-oxathiine 2,2-dioxides

A series of 6-styryl-1,2-oxathiine 2,2-dioxides have been efficiently obtained by a two-step protocol from readily available (1E,4E)-1-(dimethylamino)-5-arylpenta-1,4-dien-3-ones involving a regioselective sulfene addition and subsequent Cope elimination. Pd-Mediated direct C-H bond functionalisation of the 6-styryl-1,2-oxathiine 2,2-dioxides and a wider selection of 5,6-diaryl substituted 1,2-oxathiine 2,2-dioxides proceeded smoothly to afford C-3 (hetero)aryl substituted analogues and the results are contrasted with those of a complementary bromination - Suzuki cross-coupling sequence. Whilst the cycloaddition of benzyne, derived from in situ fluoride initiated decomposition of 2-(trimethylsilyl)phenyl trifluoromethanesulfonate, to the substituted 1,2-oxathiine 2,2-dioxides resulted in low yields of substituted naphthalenes, the addition of 4-phenyl-1,2,4-triazoline-3,5-dione to the 6-styryl-1,2-oxathiine 2,2-dioxides afforded novel 5,9-dihydro-1H-[1,2]oxathiino[5,6-c][1,2,4]triazolo[1,2-a]pyridazine-1,3(2H)-dione 8,8-dioxides through a silica-mediated isomerisation of the initial [4 + 2] adducts.

Concerning the reactivity of PTAD with isomeric dienes: the mechanism of the Diels-Alder cycloaddition

Cyclopropyl substituted dienes are employed as mechanistic probes in the triazolinedione Diels-Alder (DA) reaction. In aprotic and protic solvents, apart from the DA adducts that bear an intact cyclopropyl group, complicated and rearranged products are also obtained. These results provide solid evidence for the involvement of an open intermediate with a lifetime greater than 2 x 10(-12) s.

Tandem Ene Addition/Diels-Alder Cycloaddition reactions of Methyl Linoleate with 4-Phenyl-1,2,4-Triazoline-3,5-Dione and Diethyl Azodicarboxylate

Treatment of methyl linoleate with 4-phenyl-1,2,4-triazoline-3,5-dione affords 1:1 adducts resulting from ene addition, and 1:2 adducts formed by ene addition followed by Diels Alder cycloaddition. The corresponding reaction of diethyl azodicarboxylate yields predominantly 1:1 ene products.