Iodonium ylides ketocarbenes from

Iodonium ylides coming from precursors with one or two keto groups react thermally or photochemically with alkenes, alkynes, nitriles and some heterocumu-lenes. The products are 5-membered heterocycles with at least one oxygen atom, as illustrated in Table 10.2. Their formation can be described as the result of a formal [3 + 2] cycloaddition from the mesomeric 1,3-dipole structure of ketocarbenes, according to the general scheme (a = b mostly ethylenic double bonds) ... 

Ketocarbenes (1) are usually generated from the corresponding diazo compounds (3).s Other sources which are occasionally used are a,a-dibromo compounds (4),9 sulfur ylides (5)10 and iodonium ylides (6 Scheme 2).11 The thermal or photochemical decomposition of diazo compounds in the presence of ir-systems is often complicated by indiscriminate side reactions, such as Wolff rearrangements,12 C—H insertions and hydride migrations. To avoid such problems, the use of metal-catalyzed decomposition of diazo compounds is generally preferred.1 2... 

Hadjiarapoglou, L.R, Xhe chemistry of photolytically and thermally generated a-ketocarbenes from iodonium ylides of [3-diketones, Tetrahedron Lett., 28, 4449, 1987. 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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