Pyrrolyl-3-carbinols

Treatment of Wacylpyrrole 1513 (R =Et) with 2.2-3.0equiv of ethylmagnesiun bromide in the presence of Ti(OPr )4 (l.l-1.5equiv) in ether at room temperature, followed by addition of D2O and subsequent aqueous work-up (or direct silica gel column chromatography), gave pyrrolyl carbinol 1514a (R = H) in 92% yield (Equation 308) <20050L2105 and... 

Condensations of pyrroles with aldehydes and ketones oceur easily by acid catalysis, but the resulting pyrrolyl-carbinols cannot usually be isolated, for under the reaction conditions proton-catalysed loss of water produces 2-alkylidene-pyrrolium cations that are themselves reactive electrophiles. Thus, in the case of pyrrole itself, reaction with aliphatic aldehydes in acid inevitably leads to resins, probably linear polymers. Reductive trapping of these cationic intermediates, producing alkylated pyrroles, can be synthetically useful, however all free positions react acyl and alkoxycarbonyl-substituents are unaffected. ... 

An interesting reactivity comparison was carried out with l-(l-methyl-2-indolyl)-l-(jV-methyl-2 -pyrrolyl)ethene 57 obtained via the corresponding carbinol. An inspection of its structure suggests that the molecule could react in a cycloaddition reaction as a vinylindole or as a 2-vinylpyrrole. In reactions with dienophiles, which include DMAD, it reacted as a 2-vinylindole, affording a carbazole derivative 58 (89JHC1869). 

Phenyl-bis(2-(5-benzoyl)pyrrolyl) methane (215 mg, 0.5 mmol) in 40 mL THF/MeOH (3 1) was reduced by 946 mg NaBH4 (25.0 mmol) to afford the corresponding carbinol, which upon being dried under vacuum for 30 min was immediately subjected to condense with 3.47 mL pyrrole (50 mmol) in the presence of 122 mg Dy(OTf)3 (0.2 mmol) in 200 mL CH2CI2 for 1.3 h at room temperature. After the addition of 0.139 mL triethylamine... 

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