Über die [3+2]‐Cycloaddition von Nitronen und Isothiocyanaten

Abstract

Die Nitrone 1 cyclisieren im allgemeinen mit Isothiocyanaten 2 zu 1,2,4-Oxadiazolidin-5-thionen 3, in seltenen Fallen jedoch zu 1,2,4-Oxadiazolidin-5-onen 4. Dinitrone des Glyoxals 8 ergeben mit Isothiocyanat (Isocyanat) die Produkte 9 bzw. 10. [3 + 2]Cydonddition Reactions of Nibones with IsothioganatesCyclisation of nitrones 1 with isothiocyanates 2 commonly leads to 1,2,4-oxadiazolidine-5-thiones 3, in some rare cases however to 1,2,4-oxadiazolidine-5-ones 4. Glyoxal dinitrones 8 undergo reaction with isothiocyanates (isocyanates) to yield the products 9 and 10, respectively. Im Gegensatz zu der umfangreichen Literatur uber [3 + 21-Cycloadditionen von Nitronen 1') und Isocyanaten 5 (zu 4) sind solche mit Isothiocyanaten 2 (zu 3) nur in bemerkenswert wenigen Fallen beschrieben, fur offenkettige Nitrone sogar nur singular fur N-Methyl-C-phenylnitron (lag) und Phenylisothiocyanat (2g)*). Die letztgenannte Reaktion konnten wir nur unter (zusatzlicher) Katalyse [z. B. durch Tributylmethoxy-

Isothiocyanates in the chemistry of heterocycles

“…262 It is noteworthy that the cycloaddition of azide ion to isothiocyanates was previously used for the preparation of 1-substituted tetrazoline-5-thiones.1 A three component reaction involving an aryl isothiocyanate, alkyl or aryl isocyanate, and alkyl azides afforded thiadiazoles 243 in good yields.263 Addition of nitrones to alkyl and aryl isothiocyanates furnished oxadiazolidinethiones 245 in variable yields (eq 58). 264 A similar reaction with cycloheptatrienylideneamine oxide was also reported. should be mentioned that cycloaddition of nitrile oxides to isothiocyanates does not seem to have been observed.…”

“…Azomethine imines with phenyl isothiocyanate afforded triazolidinethiones 258 which were found to undergo cleavage even in cold solution (eq 60). 273 Other products were less vulnerable.1 Thus, the reaction of isothiocyanates with 259 furnished imidazolidinethiones (260) 261 formed only a simple adduct 262 (eq 62),275 whereas the ylide 263 with phenyl isothiocyanate gave imidazopyridines 264 (eq 63). 276 2-Methyloxirane, aided by complexes of tin halide and Lewis bases, added to benzyl isothiocyanate to give…”

Synthesis and Ring Opening Reactions of Tetrahydroimidazo[1,5- b ][1,2,4]oxadiazol-2(1 H )-thiones

“…Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. 7 We have shown the 1,3-dipolar cycloaddition reactions of cyclic nitrones 1 with dipolarophiles as arylisocyanates, 8,9 styrene, 10 DMAD, 11,12 and β-pinene 13 to proceed regio and in the case of chiral nitrones diastereoselectively. 1 1,3-Dipolar cycloadditions of nitrones with variety of dipolarophiles take an important place among the methods for the synthesis of five membered heterocyclic compounds.…”

“…6 The reaction of acyclic nitrones with isothiocyanates was shown to give mainly oxadiazolidin-5-thiones. 7 We have shown the 1,3-dipolar cycloaddition reactions of cyclic nitrones 1 with dipolarophiles as arylisocyanates, 8−9 styrene, 10 DMAD, 11−12 and β-pinene 13 to proceed regio-and, in the case of chiral nitrones, diastereoselectively. When heated, the adducts from isocyanates and styrene undergo retro 1,3-dipolar cycloaddition, while the adducts from DMAD and β-pinene give the corresponding imidazoles.…”

Revealing Stepwise Mechanisms in Dipolar Cycloaddition Reactions: Computational Study of the Reaction between Nitrones and Isocyanates

“…1,3-Dipolar cycloadditions between nitrones and alkenes are well-known reactions of considerable interest since the resulting isoxazolidines are versatile synthetic intermediates in the preparation of a variety of natural and related compounds . In addition to alkenes, nitrones also react with allenes and heteroallenes such as ketenes, , isothiocyanates, and isocyanates . Depending on the type of compound one or both double bonds of the allene can participate in the cycloaddition reaction.…”