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A series of 6-styryl-1,2-oxathiine 2,2-dioxides have been efficiently obtained by a two-step protocol from readily available (1
E
,4
E
)-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-1
H
-[1,2]oxathiino[5,6-
c
][1,2,4]triazolo[1,2-
a
]pyridazine-1,3(2
H
)-dione 8,8-dioxides through a silica-mediated isomerisation of the initial [4 + 2] adducts.
1,2-Oxathiine 2,2-dioxides readily undergo C-H activated coupling at C-3. The 6-styryl derivatives participate in cycloadditions with PTAD to afford 1
H
-[1,2]oxathiino[5,6-
c
][1,2,4]triazolo[1,2-
a
]pyridazine-1,3(2
H
)-dione 8,8-dioxides.