Ketenimine intermediate

The sulfonamide (30) undergoes a clean, uncatalysed deep-seated rearrangement to sulfone (31) via a ketenimine intermediate, a rearrangement in which both the / -toluenesulfonyl (Ts) and p-methoxybenzyl (PMB) groups sequentially migrate from the nitrogen atom on to a neighbouring carbon at the /3-position.51... 

The silylated lithium ynamine 192 is generated by metaUation with BuLi of 5 -methyl Af-phenyl-trimethylsilylethanimidothioate (190), via a ketenimine intermediate (191), as shown in equation 75. The interconversion between 191 and 192 can be discerned by silylation taking place at both the N- and -positions to afford the Af-silylynamide 193 and the bis(/ -silyl)ketenimine 194. In equation 76 are shown three possible synthetic... 

The bicyclic compound (222) and its angularly fused benzologue (223) can be obtained from phosphoranylidene compounds (221), in excellent yields using 2 mol of diphenylketene (Equation (46)). The reactions are thought to proceed via ketenimine intermediates <80ZC2ii, 86ZCioo>. 

Scheme 10.8 (a) Products of CuAAC reactions with sulfonyl azides, (b) Possible pathways leading to ketenimine intermediates. 

A number of reports concern the attack of nucleophiles on perfluoro-olefins to give cumulenes or heterocumulenes, which in turn imdergo nucleophilic attack to give heterocyclic compounds with perfluoroalkyi substituents. o-Phenylenedi-amine reacts with hexafluoropropene to give 2-(o j8j8>tetrafluoroethyl)benzimidazole (301) ketenimine intermediates have also been utilized in the formation of quinolines (302) (see p. lll) 89.59o j,y intramolecular cyclization, and (303) (see p. 112) by intermolecular cyclization, naphthyridines (304), pyridopyrimidines (305), and isoquinolines (306). The pyran derivative (307) is formed via isomerization of an allene intermediate (see p. 100). 3-Fluoro-2-isopropyl-l,2,4-thiadiazolin-... 

At-Tosylhydrazones, R R C=NNHTs, undergo a palladium-catalysed amidation with isocyanides (CN-R ) via a ketenimine intermediate in the presence of water. This allows access to amides, R R HC-CONHR , from carbonyl compounds via a one-carbon extension. ... 

An interesting Cu(I)-catalyzed annulation of tethered pyrroloalkynes 365 and 367 into amino-substituted N-fused pyrroloheterocycles 366 and 368, respectively, was recently demonstrated by Chang (Scheme 9.128) [306]. This reaction was proposed to proceed through a ketenimine intermediate 370, which in turn was generated in situ from the 1,2,3-triazole cycloadduct 369 upon extrusion of dinitrogen (Scheme 9.129). 

A three-component reaction for the synthesis of functionalized benzimidazoles from terminal alkynes, o-aminoanilines, and / -tolylsulfonyl azide is developed by Wang and coworkers (Scheme 8.52). The C(sp)-H bond of alkyne was activated in this reaction via Cul-catalyzed azide-alkyne cycloaddtion (CuAAC) reaction which could lead to the formation of a ketenimine intermediate by the release of N2- The benzimidazoles could be obtained by intramolecular nucleophilic addition and subsequent elimination of amide intermediate with 2% H2SO4 under reflux conditions [91]. They also developed another protocol for the synthesis of substituted benzimidazole derivatives via a sequential three-component cascade reaction from sulfonyl azides, alkynes, and 2-bromoanilines using Cul as catalyst. Similarly, the C-H bond of alkyne was activated at the process of copper-catalyzed azide-alkyne cycloaddtion (CuAAC) reaction [92]. 

SCHEME 5.56 Cu(I)-catalyzed formation of the ketenimine intermediate from sulfonyl azide and terminal aUcyne. 

The oxime 299 is silylated in the presence of catalytic amounts of TMSOTf 20 to 300, which affords, via the Beckmann fragmentation intermediate 301 and alkylation with allyltrimethylsilane 82, 66% of the seco nitrile 302 [101, 102] (Scheme 4.39). Tris(trimethylsilyl) ketenimine 303 reacts with aldehydes such as benzaldehyde in the presence of Bp3-OEt2, via the aldol adduct 304, to give the unsaturated nitriles 305, in 99% yield, and HMDSO 7 [103]. 

An unusual domino process was observed by Biehl and coworkers [69] in the reaction of 2-bromo-l-naphthol 4-196 with arylacetonitriles in the presence of LDA or LiTMP by employing 3-thienylacetonitrile 4-197, the tetracyclic compound 4-200 was obtained in 57% yield (Scheme 4.43). The reaction probably includes the formation of an aryne and a ketenimine which undergo [2+2] cycloaddition to give 4-198, followed by rearrangement and allylic addition to the intermediately formed aryl cyano compound 4-199. 

The (aziridin-l-ylimino)phosphoranes (57) react with ketens to give nitrile derivatives, presumably from an intermediate ketenimine by breaking the N—N bond and migration of the aziridinyl group.60 They also react with acyl halides and... 

Another preparation of oxadiazoles proceeds from N-acylaminoimino-phosphorane as well. With diphenylketene, an intermediate ketenimine (155) is converted to 2-diphenylmethyl-l,3,4-oxadiazole 156 (Scheme 61) [91PS(63)283]. 

Carbene complexes undergo benzannulation under photochemical conditions with carbon monoxide to give the indolocarbazoles via a ketene intermediate, or aminobenzannulation with /t-butyl isonitrile under thermal conditions via a ketenimine (Equation (77) Table 3) <1997TL6787, 2001T5199>. 

This finding led to general acceptance of the view that either azirine (29) and/or ketenimine (30) are the trappable reactive intermediates produced upon photolysis of phenyl azide in solution. ... 

Schrock and Schuster confirmed and extended this work using LFP techniques in 1984. Schuster and co-workers later employed flash photolysis with IR detection to confirm that ketenimine 30 is the reactive intermediate present on the microsecond time scale. 

The cyclic ketenimine 30 is the major trappable reactive intermediate present in solution when phenyl azide (at moderate concentrations) is decomposed photolyti-cally at 298 K. The rate of decay of singlet phenylnitrene 33s is equal to the rate of formation of the cychc ketenimine. The first step, cyclization to benzazirine (29) is rate determining, and is followed by fast electrocyclic ring opening to cychc ketenimine 30. 

As mentioned previously, unique kinetic results were obtained upon LFP of o-fluorophenyl azide,in that the singlet nitrene decays faster than the ketenimine is formed. This finding requires the presence of an intermediate, presumably ben-zazirine 40, between the singlet nitrene and ketenimine 42. The data could be interpreted by assuming that azirine 40 reverts easily to singlet nitrene according to the scheme below.The equilibrium constant is equal to the ratio of [40]/[39s] and was deduced to be 0.5 with AG 350 caFmol. Younger and Bell have also reported a system in which a benzazirine and ketenimine interconvert. 

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