Formation of pyrrole derivatives

Scheme 11.13 Formation of pyrrole derivatives via iminyl radical cyclization on to a cumulated Jt-bond [68]. a X = S-C(NCH3)(SCH3).

There are no reports in the literature of the formation of pyrrole derivatives by the oxidative degradation of the o-quinone rings of the simple aminochromes. However, several pyrrolecarboxylic acids have been obtained on oxidation of the melanins, which are considered by some authors to contain aminochrome units in the polymer (cf. ref. 168), (see Section V, A), and pyrrole-2,3,5-tricarboxylic acid has been... 

The formation of pyrrole derivatives has been reported earlier. The triazoline (392) was converted by heating at its melting point into the 4-oxazoline (393) which in turn gives the 2,5-dihydropyrrole (394) on reaction with ethyl acetylenedicarboxylate (70CR(C)(27i)9S8). 

A novel extrusion of sulphur dioxide has been reported on irradiation of the 2,5-diaryl-1,4-dithiine 1,1-dioxides (156) to give the thiophenes (157) and (158) in low yields the exact stage at which sulphur dioxide is lost is uncertain, but the intermediacy of species such as (159) or (160) is supported by the formation of pyrrole derivatives in the presence of n-butylamine. 

Knorr pyrrole synthesis. Formation of pyrrole derivatives by condensation of a-amino ketones as such or generated in situ from isonitrosoke-tones with carbonyl compounds containing active ot-methylene groups. 

Although the chemistry of a-diazocarbonyl compounds have been extensively investigated the formation of pyrrole derivatives from a-diazo carbon bearing 5-(N-tosyl)amine group in unprecedented. The Rh2(OAc)2-catalyzed reaction of diazo 1,3-diketone 242 gives pyrrole derivatives (243) via intramolecular N-H insertion.83... 

A novel extrusion of S02 is reported for the dithiine dioxides 104 to afford low yields of the thiophenes 105 and 106. The exact step at which the S02 loss occurs is not known but the proposed intermediates 107 and/or 108 have support from the formation of pyrrole derivatives when the reaction is carried out in the presence of n-butylamine103. Sunlight-induced extrusion of sulphur dioxide from the pyranone dioxide 109 is similar to the above and results in the formation of the reactive cyclopentadienone 110 which can be trapped by dienophiles or in their absence forms a trimer104. The platinum complex 111 is photochemically labile and decomposes into benzyne on irradiation105. 

Formation of pyrrole derivatives from a-chloromethyl ketones, (3-keto esters and ammonia or amines ... 

On the other hand, the reaction of the propargylic alcohol with dibenzoylmethane was performed in the presence of a catalytic amount of [Ir(cod)(p-Cl)]2 and SnCl followed by addition of aniline, and the reaction was performed at 80 °C which led to the formation of pyrrole derivatives in 78% yield (Scheme 11.21). 

Tilley and coworkers have reported a general and efficient method for the synthesis of various functionalized thiophene-1-oxide derivatives, via the reaction of zirconacyclopentadienes with SO2 [65]. Thiophenes were also obtained by the reaction of zirconacyclopentadienes with S2CI2 [66]. When ni-trosobenzene was used, Lewis acids were found to be effective for the promotion of formation of pyrrole derivatives from the reaction of zirconacyclopentadienes with nitrosobenzene (Eq. 58) [67]. 

Hantzsch synthesis The formation of pyridine derivatives by the condensation of ethyl acetoacetate with ammonia and an aldehyde. Also applied to similar syntheses of pyrroles. 

These reactions are related to the formation of pyrroles and quinolines from aminocarbonyl compounds and acetylenes (582,583) and may be contrasted with the formation of pyran derivatives by electrophilic attack on an enamine, followed by addition of an oxygen function to the imonium carbon (584-590). 

The addition of trithiazyl trichloride (NSC1)3 to 2,5-disubstituted furans and to N-2,5-trisubstituted pyrroles has led to the formation of isothiazole derivatives <96JHC1419>. 

Again, rhodium-complexes, although in a completely different process, catalyzed the formation of indolizidine derivatives through the hydroformylation of pyrroles bearing a terminal double bond. The intermediate aldehyde reacted to afford the final product 74 (Scheme 23) <2004TA1821>. 

The rearrangements of Diels-Alder-derived sulfmamides have been examined for the formation of pyrroles < 19%CHEC-II(6)349>. Recently the [4+2] cycloadduct 161 was shown to undergo this rearrangement under mild conditions affording the pyrrole 162 in excellent yield (Equation 26) <2003T9669>, see also <2004TL7553> and <1994SC175>. 

Erba et al. (102) observed a novel formation of pyrrole imines 181 from the 1,3-dipolar cycloaddition of mtinchnones 179 and 5-amino-l-aryl-4,5-dihydro-4-methylene-1,2,3-triazoles 180 (Table 10.4). Treatment with benzaldehyde yielded 3-formylpyrroles (182). The reaction presumably involves loss of carbon dioxide, nitrogen, and morpholine from the initial cycloadduct. Unsymmetrical mtinchnones behave regioselectively and furnish products derived from bonding between C(2) of... 

Another class of pyrrole derivative may be obtained by the interaction of l-amino-l-deoxy-2-ketoses or 2-amino-2-deoxyaldoses with a jQ-dicarbonyl compound. Unlike the previous type (which is N-substituted), these pyrrole derivatives have a tetrahydroxybutyl group in the a- or /8-position with respect to the nitrogen atom of the ring, in addition to other groups arising from the dicarbonyl compound used in the condensation. The formation and reactions of this type of pyrrole derivative have been discussed in detail in two articles in this series48,49 they will, therefore, only be treated briefly. 1-Amino-l-deoxy-D-fructose (53) reacts with 2,4-pentanedione to give50 pyrrole derivative 54a similar pyrroles were obtained with ethyl acetoace-tate,50,51 which yields 54b. 

Another interesting formation of 6H-1,3-oxazin-6-one derivatives by the oxidation of pyrrole derivatives was described by Sprio215 [Eq. (57)] (see also Yee et a/.216). 

The first mechanism is favored at present (see Sections IV.A-C) in many cases the formation of pyrroles clearly involves O-vinyl derivatives. 

Side reactions became even more prevalent when 2-methyl-A -BOC-pyrrole 1046 was used as substrate (the addition of the methyl group increased the electronic density on the pyrrole and this led to enhanced formation of products derived from zwitterionic intermediates) (Equation 247). Thus, rhodium(ll) octanoate-catalyzed decomposition of diazoalkane 1042 in the presence of pyrrole 1046 resulted in the formation of three types of products two isomeric tropanes, 1047 (38% and 56% for R = Me and R = EtC02CH2, respectively) and 1048 (16% and 8% for R = Me and R = EtC02CH2, respectively), as well as two other products, the l,3a,6,6a-tetrahydrocyclopenta[ ]pyr-role 1049 (10% and 8% for R = Me and R = EtC02CH2, respectively) and the 7-azabicyclo[4.2.0]octa-2,4-diene 1050 (27% and 12% for R = Me and R = EtC02CH2, respectively) <1995TL7205>. 

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