2- Butyl pyrrole

The reaction of pyrrole with ethylmagnesium bromide gives the magnesium salt of pyrrole. This, in turn, reacts with (-)-2-bromobutane to give a mixture of 2-and 3-(2-butyl)pyrrole. Oxidation of the mixture gives (+)-2-methylbutyric acid. Describe how you could determine the stereochemical course (inversion or retention) of the coupling reaction. 

The octahydroindolizine trail pheromone (412) of the Pharaoh ant (Monomorium pharaonis) was first prepared by Ritter et al. (181) as a mixture of stereoisomers, beginning with a termolecular condensation (Scheme 74). Oliver and Sonnet (182) then unambiguously synthesized the four stereoisomers from 2,6-lutidine (413) (Scheme 75) and 2-butyl-pyrrole (418) (Scheme 76). 

Cobalt complex 83 was obtained by the reaction of [CpCo(SMe2)3l2(BF4)2 with pentamethylpyrrole [88AG(E)579]. Full cobalt sandwich of 2,5-di-terr-butyl-pyrrole is also known [91JCS(CC)1368]. Meanwhile, attempts to synthesize other pyrrolyl complexes of cobalt, (Ti -2,5-dimethylpyrrole)cobalttricarbonyl and the 3,4-dimethyl analog, have been unsuccessful [87JOM(330)231]. 

Much more studied is the reaction of /8-dicarbonyl compounds with 2-amino-2-deoxyaldoses in particular, with 2-amino-2-deoxy-D-glu-cose (55), both in neutral and alkaline medium. In neutral methanol or aqueous acetone, 2-amino-2-deoxy-D-glucose reacts with 2,4-pen-tanedione to give52 54 3-acetyl-2-methyl-5-(D-arabino-tetrahydroxy-butyl)pyrrole (56a), and, with ethyl acetoacetate,55 the pyrrole 56b. Similar (tetrahydroxybutyl)pyrroles have been prepared from other /3-keto esters, such as ethyl 3-oxohexanoate, ethyl thiolacetoacetate, and diethyl 3-oxopentanedioate.53,56,56a... 

High yields of hydroperoxypyrrolenines like (30) (Section III) were obtained by photo-oxidation of hindered pyrroles, such as 2,5-di- and 2,3,5-tri-<-butyl-pyrroles.125 The autoxidation of 2,4-dimethyl-pyrrol-5-ethyluretane yielded 50% of the hydroxyderivative (100).126 A series of tetra-arylpyrroles carrying substituents on the 2 and 5 aryl groups were oxidized with lead dioxide and the stability of corresponding free... 

The fact that the percentage of jS-aldehydes from Vilsmeier formylation of N-alkylpyrroles increases from M-methyl- to N-(f-butyl)pyrrole can be explained by the increasing steric shielding of the a-positions by an N-alkyl group in the same sequence (70JCS(C)2563) (Scheme 23). 

Table 3 Total energies of cationic tr-complexes formed from pyrrole, N-methylpyrrole, and N-(tert-butyl)pyrrole on addition of trimethylsilyl cation at a- ( j and -positions ( ) as well as values characterizing preferable site of electrophilic attack... 

K.12) l//-Pyrrole, l-(2-methylbutyl)-, 1 -(2-methylbutyl)pyrrole, I-(sec-butyl)pyrrole, N-(2-methylbutyl)pyrrole (13678-55-2]... 

The reaction of 1-amino-l-deoxy-D-fructose with ethyl thiolacetoacetate under the same conditions gives a mixture of ethyl 2-methyl-4-(D-ara6ino-tetrahydroxybutyl)pyrrole-3-carbothiolate (18), a lactone [tentatively considered to be the 7-lactone (27) of 2-methyl-4-(D-aroWno-tetrahydroxy-butyl)pyrrole-3-carboxylic acid (19)], and a small proportion of a com-... 

Ethyl 2-methyl-4-(D-ara6mo-tetrahydroxybutyl)pyrrole-3-carbothiolate (18) yields a tetra-O-acetyl derivative, and, on oxidation with periodic acid, affords ethyl 4-formyl-2-methylpyrrole-3-carbothiolate (22). Lactone (27) gives a tri-O-acetyl derivative and, on alkaline hydrolysis, consumes one equivalent of base and furnishes 2-methyl-4-(D-arofemo-tetrahydroxy-butyl)pyrrole-3-carboxylic acid (19) in almost quantitative yield. This acid can, in turn, be transformed into a tetra-O-acetyl derivative, and, when oxidized with sodium metaperiodate, it gives 4-formyl-2-methyl-pyrrole-3-carboxylic acid (23). Attempts to determine the size of the lactone ring in compound (27) by oxidation with sodium metaperiodate were unsuccessful three moles of metaperiodate were consumed per mole, as if, during the oxidation, hydrolysis of the lactone had occurred. 

Figure 11.19. Chemical stmcture of pyrrole/3-[4-(2,5-di-methoxyphenyl)butyl]pyrrole copolymer.

With the specific objective here being the preparation of redox-active films of ferrocene covalently bonded to polypyrrole, the first task is to attach the ferrocene moiety to either the 3-alkyl or the 1 -alkyl of pyrrole and the second task is to copolymerize the ferrocene derivatized pyrrole (Fc-P) with pyrrole. The synthesis of a typical ferrocene-3-alkyIpyrrole monomer is described elsewhere [151] and Merz and co-workers [152] give a procedure for preparing A -(4-ferrocenyl-butyl)pyrrole (PFc04). 

Methyl-5.[D.arabotetraoxy.butyl].pyrrol-carb aure.(3)-athylester 22 II 7. 

It is also of significance that in the dilute gas phase, where the intrinsic orientating properties of pyrrole can be examined without the complication of variable phenomena such as solvation, ion-pairing and catalyst attendant on electrophilic substitution reactions in solution, preferential /3-attack on pyrrole occurs. In gas phase t-butylation, the relative order of reactivity at /3-carbon, a-carbon and nitrogen is 10.3 3.0 1.0 (81CC1177). 

A comparison of the relative basicities of pyrrole, furan and thiophene may be made by comparing the pK values of their 2,5-di-t-butyl derivatives, which were found to be -1.01, —10.01 and —10.16, respectively. In each case protonation was shown by NMR to occur at position 2. The base-strengthening effect of alkyl substitution is clearly apparent by comparison of pyrrole and its alkyl derivatives, e.g. A-methylpyrrole has a pKa. for a-protonation of -2.9 and 2,3,4,5-tetramethylpyrrole has a pK of 4-3.7. In general, protonation of a-alkylpyrroles occurs at the a -position whereas /3-alkylpyrroles are protonated at the adjacent a-position. As expected, electron-withdrawing groups are base-weakening thus A-phenylpyrrole is reported to have a p/sTa of -5.8. The IR spectrum of the hydrochloride of 2-formylpyrrole indicates that protonation occurs mainly at the carbonyl oxygen atom and only to a limited extent at C-5. 

X-ray, 4, 160 (79AX(B)2228> lH-Pyrrole-2,4-diamine, 1-t-butyl-JV, JV -dimethyl-3-phenyl-JV -phenylsulfonyl-X-ray, 4, 160 (78BSB893) lH-Pyrrole-3-methanol, 4-acetyl-X-ray, 4, 160 (78AX(B)1248> lH-Pyrrole-3-methanol, 4-acetyl-, hydrate X-ray, 4, 160 (78AX(B)1248> lH-Pyrrole-3-propanoic acid, ester C NMR, 4, 172 (74JCS(P2)1004>... 

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