Pyrroles silver® fluoride

Quinones have also been used as dipolarophiles, giving pyrrole derivatives after oxidation with excess silver fluoride. Reineta isoindole, a naturally occurring antimicrobial compound, was synthesized by this route in good yield.444... 

IV-silylmethyl a-cyanoimines have been studied as a precursor of nitrile ylids. They undergo facile cycloaddition with dipolarophiles. Thus reaction with DM AD in the presence of silver fluoride leads to the formation of the corresponding pyrrole derivative in good yield, but no reaction occurs with the non-activated n-bond of styrene.453... 

Azomethine ylides can also be generated from a-cyano- or a-phenylthiomethylamines <85JOC4006, 86CB813). Silver fluoride promotes the elimination. The adducts from alkynes are 2,5-dihydropyrroles which can be oxidized to pyrroles by ddq (Scheme 82). 

While most [3+2] cycloaddition reactions with indoles employ the indole moiety as the dipolarophile comptment, several reports have also highlighted the utility of indoles as the source of dipoles in 1,3-dipolar cycloaddition reactions. Padwa and coworkers produced early examples in which the indole pyrrole ring acted as an azomethine ylide dipole [94, 95]. Treatment of a silylated indole 235a with silver fluoride in the presence of a variety of dipolarophiles 236 and 238 afforded the corresponding cycloadducts 237 and 239 in 53% and 83% yield, respectively (Scheme 63). 

Interestingly, heating a solution of 235b with DMAD (61) and silver fluoride at 80°C produced pyrrole 237 in 75% yield (Scheme 64). The conversion of 235 to 237 probably proceeds via the intermediacy of the [3+2] cycloadduct 236, which undergoes a subsequent 1,5-hydrogen shift under the reaction conditions to give 237. 

A mixture of silver(I) fluoride and 2,2 -bipyridine replaces chlorine with fluorine in 1-chloro-octane in 86% yield after 45 minutes at 130°C.28 Some heterocyclic polychloro derivatives are also fluorinatcd by silver(I) fluoride. Thus, perfluoro(2,3,4,5-tetrahydropyridine) (1) and per-fluoro(3,4-dihydro-2//-pyrrole) are prepared from 2,2,6-trichloro-3,3,4,4,5,5-hexafluoro-2,3.4,5-tetrahydropyridine and 2,2,5-trichloro-3,3,4.4-tetrafluoro-3,4-dihydro-2//-pyrrole by reaction with silver(l) fluoride at room temperature.31 Since the fluorination of 2,2,5-trichloro-3,3,4,4-tetrafluoro-3,4-dihydro-2//-pyrrole with silver(l) fluoride is slow, recycling is necessary.31... 

Pentachloro-2//-pyrrole (21) was converted to the trifluoro derivative 143 by excess silver(I) fluoride at 135°C57 and to the salts 144 with N,N-dimethyl(trimethyl)silylamine (R = Cl or NMe2, depending on the amount... 

The use of ozonolysis to establish the structure of pentamethyl-2//-pyrrole (1) was described earlier (Section II,A,2).16 Treatment of pentachloro-2f/-pyrrole with silver(I) fluoride gave in addition to the fluoride (143), the bis(acid fluoride) of dichloromaleic acid.57 Oxidation of the diamino ester 155 with lead tetraacetate led to the cyanoimine 156, which in turn was cyclized to the pyrimidine 157 (Scheme 54).137... 

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