- [3+2] cycloadditions of n-protected '(S)-Diazoproline' with selected acetylenes
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Acetylene carboxylates and an acetylene phosphonate reacted with N-protected (S)-2-(diazoacetyl)pyrrolidines ((S)-diazoprolines) to give optically active bis-heterocyclic pyrazole derivatives in a regioselective [3+2] cycloaddition. The reactions occurred
- Mlostoń, Grzegorz,Pipiak, Paulina,Heimgartner, Heinz
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p. 223 - 231
(2017/07/28)
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- Mechanistic Studies on the Wolff Rearrangement: The Chemistry and Spectroscopy of Some α-Ketocarbenes
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Photochemical extrusion of dinitrogen from diazo ketones 1-4 matrix isolated in argon at 10-15 K produces α-ketocarbenes 5, 6, and 8.UV-vis, infrared, and electron spin resonance spectroscopy identify the α-ketocarbenes, which are further characterized by trapping with carbon monoxide and dioxygen.Excitation (T0-T1) of the α-ketocarbenes leads to rapid ring contraction of 5 -> 9 and slow ring contraction of 6 -> 10 and 8 -> 12.This trend parallels the increasing degree of strain in the product ketenes.Shorter wavelength irradiation causes rapid ring contraction of 6 -> 10 and 8 -> 12.The stepwise Wolff rearrangement of 1-4 proceeds through an α-ketocarbene.Ring contraction occurs in a singlet excited state (S''') formed upon photolysis of the primary product α-ketocarbene (T0).
- McMahon, Robert J.,Chapman, Orville L.,Hayes, Richard A.,Hess, Thomas C.,Krimmer, Hans-Peter
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p. 7597 - 7606
(2007/10/02)
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- Ramberg-Baecklund Reaction of 1,3-Dibromo-1H,3H-naphthothiopyran 2,2-Dioxide. Formation of Acenaphthyne Intermediate
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Radical bromination of 1H,3H-naphthothiopyran 2,2-dioxide (15) gave the corresponding monobromo sulfone 16 (48percent), dibromo sulfone 12 (43percent; cis/trans = 64/36), and tribromo sulfone 17 (5percent).Ramberg-Baecklund reaction of 12 was investigated under a variety of coditions with expectation of the formation of thiirene dioxide 11 from which generation of acenaphthyne (5) would be expected both thermally and photochemically.Observed characteristic features of the reaction are as follows: (i) the use of triethylamine as base yielded 1-bromo-acenaphthylene (20; 39percent) and debrominated products 15 (5percent) and 16 (9percent); (ii) the use of sodium methoxide as base afforded decacyclene (3) surprisingly, though in a trace amount, in addition to 20 (75percent) and acenaphthylene (18; 9percent); (iii) the use of potassium tert-butoxide as base gave an improved yield of 3 (5percent) along with 20 (36percent) and 18 (27percent).The formation of 3 may best be rationalized by assuming the generation of acenaphthyne intermediate 5 from 11 by loss of sulfur dioxide.
- Nakayama, Juzo,Ohshima, Etsuo,Ishii, Akihiko,Hoshino, Masamatsu
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