Acetone pyrrole ketones

Pyrroles react with the conjugate acids of aldehydes and ketones to give carbinols (e.g. 67) which cannot normally be isolated but which undergo proton-catalyzed loss of water to give reactive electrophiles (e.g. 68). Subsequent reaction may lead to polymeric products, but in the case of reaction of pyrrole and acetone a cyclic tetramer (69) is formed in high yield. 

The unsaturated tetraoxaquaterene (accompanied by linear condensation products) was first synthesized in 18.5% yield by the acid-catalyzed condensation of furan with acetone in the absence of added lithium salts. Other ketones also condensed with furan to give analogous products in 6-12% yield.A corresponding macrocycle was also prepared in 9% yield from pyrrole and cyclohexanone. The macrocyclic ether products have also been obtained by condensation of short linear condensation products having 2, 3, or 4 furan rings with a carbonyl compound. ... 

Thus, pyrrole and acetone react as shown above. This involves pyrrole acting as the nucleophile to attack the protonated ketone in an aldol-like reaction. This is followed by elimination of water, facilitated by the acidic conditions. This gives an intermediate alkylidene pyrrolium cation, a highly reactive electrophile that reacts with another molecule of nucleophilic pyrrole. We then have a repeat sequence of reactions, in which further acetone and pyrrole molecules are incorporated. The presence of the two methyl substituents from acetone forces the growing polymer to adopt a planar array, and this eventually leads to a cyclic tetramer, the terminal pyrrole attacking the alkylidene pyrrolium cation at the other end of the chain. 

Pyrrole reacts with aldehydes and ketones and an acid catalyst to form resins, probably linear polymers however, surprisingly, from an entrop-ic point of view, with acetone (propanone) and hydrochloric acid the product is a cyclic tetramer. Possibly the two methyl groups in the developing side chains force it to bend and thus bite its own tail (Scheme 6.7). 

The acid-catalyzed addition of aliphatic ketones to 2,3,4- or 2,3,5-trisubstituted pyrroles generally produces bispyrrolylalkanes, analogous in structure to the products of the corresponding reactions with aldehydes, whereas 2,5-disubstituted pyrroles react with acetone to form a 2 3 adduct (113). Pyrrole and 3,4-disubstituted pyrroles react with aliphatic ketones to give porphyrinogens (114), which, unlike the macrocycles obtained from the... 

Vibrational spectroscopy, too, has been used to study supercritical fluid systems. Buback reviewed (59) this area however, much of his discussions are on fluid systems that are well removed from ambient conditions or difficult to handle easily (e.g., H20, HC1). In an early report, Hyatt (21) used IR absorbance spectroscopy to determine the influence of several solvent systems, including COz, on the vibrational frequencies ( ) of solute molecules. Specifically, he studied the vc=o of acetone and cyclohexanone and vs.H of pyrrole. The goal of this work was to determine the suitability of supercritical fluids as reaction solvent. Hyatt concluded that the ketones experienced an environment similar to nonpolar hydrocarbons in COz and that there were no differences between liquid and supercritical CO2. In contrast, the pyrrole studies indicated that the solvent strength of CO2 was between ether and ethyl acetate. This apparent anomalous result was a manifestation of the, albeit weak, degree of pyrrole hydrogen bonding to CO2. 

Robinson s synthesis of tropine (210) on the other hand was as direct (two steps) as Willstatter s was long but it involved the use of the very sensitive succinic dialdehyde (from pyrrole) (157, 219). The fragments from the hypothetical fission of the symmetrical tropinone (XLVI) suggested to Robinson the possibility of obtaining this ketone by the condensation of succinic dialdehyde and methylamine with acetone. The primary reaction was considered to be the combination of succinic dialdehyde with methyl-amine and the resulting biscarbinolamine (XLIX) in turn condensed with acetone. This synthesis was realized when these reactants, in aqueous... 

For the first time we report the synthesis of macrocycles like calixpyrrole, cyclotriveratrylene (CTV), cyclotetraveratrylene (CTTV), porphyrine ete over molecular sieve as a catalyst. Calixpyrroles are synthesized from pyrrole and a ketone like acetone over MCM-41 under reflux conditions using suitable solvent. In case of MCM-41 cyclic calixpyrroles were obtained. On the other hand due to shape selectivity in case of Y zeolite linear di-, tri- and tetra- polypyrroles were obtained and cyclic tetramers were not observed. The mechanism of the synthesis of calixpyrrole is either by the dimerization of dimer with simultaneous cyclization to cyclic tetramer or cyclization of linear tetramer via recoil phenomenon. 

The products usually obtained from a pyrrole and an aldehyde or ketone under acid conditions are the dipyrrylmethanes, formed by further reaction of the initial carbinol with a second molecule of the pyrrole. Some examples are the formation of (18) and (19) from propionaldehyde and acetaldehyde with zinc chloride , of (20) from acetone with hydrochloric acid , and of (21) using formalin containing formic acid . Similarly, glyoxal can be used... 

New calix[4]pyrroles 145 bearing dipyrrolylquinoxaline as strapping elements have been synthesized (Kim et al. 2009). The synthesis of receptor 145 starts with ketone 142, a species that was prepared by the reaction of oxalyl chloride with 2 equivalents of 2-(3-oxobutyl)pyrrole (Yadav et al. 2001). Once in hand, 142 was reacted with 4-nitro-1,2-DAB in the presence of acid to afford bisketone 143 in 24 % yield (Black et al. 1999 Anzenbacher et al. 2000). Treatment of this latter intermediate with neat pyrrole in the presence of trilluoroacelic acid afforded the bis-dipyrromethane 144 in 74 % yield (Scheme 5.34). While this procedure proved effective, attempts to effect the direct alkylation of 6-nitro-2,3-di(2 -pyrrolyl)qui-noxaline with methyl vinyl ketone produced only trace quantities of the desired product 144. Acid-catalyzed condensation of 144 with acetone then gave the... 

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