Acetone pyrrole aldehydes

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. 

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... 

This procedure provides a method for functionalizing the pyrrole ring 1n the 3-pos1t1on, normally a difficult synthetic step when conventional electrophilic substitution is used. The technique has been extended to addition of several aldehydes and acetone and to a number of pyrroles.4 The generality Includes photoaddition to imidazoles which are substituted in the 4-posltion. Pyrrole photoadduct alcohols are readily dehydrated to 3-alkenylpyrroles or oxidized to 3-acyl derivatives. 

The increase in yield of 15 a from ca 20% to over 40% in the presence of lithium perchlorate 77) has led to the suggestion of a template effect. However, recent experiments78) indicate that the higher yields correlate not with the metal ion but with the acidity of the reaction medium. In similar fashion, thiophene and pyrrole undergo acid-catalyzed condensations with acetone to yield 16 m> and 17 81). Benz-aldehyde also condenses with pyrrole 82but the initially formed compound loses six hydrogens to form the planar tetraphenylporphin 18. 

Among other carbonyl compounds successfully used in olefin synthesis are (40), (41), the optically active dione (42), the pyrroles (43), and the xanthone (44). In the last case the aldehyde was added rapidly to a large excess of the ylide, followed immediately by acetone to remove the excess reagent. 

C02Me, etc.) have been prepared by bis-condensations between the appropriate pyrrole bis-aldehyde and substituted acetone l,3-dimethyl-2/f-cyclohepta[c]pyrrol-6-one (148 R = H, R = R = Me, X = H) was then converted into 6-ethoxy-l,3-dimethyl-2-aza-azulene, ... 

The reaction of pyrroles with two free a-positions with aldehydes occurs between four molecules of aldehyde and four pyrroles and leads to cyclic condensation products (which is the basis of a simple porphyrin synthesis, cf p. 553). Acetone reacts in a similar manner with four pyrrole units to give a cycHc tetramer 24 directly in high yield by a hydroxyalkylation/alkylation sequence [105] ... 

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... 

Rahm et al. describes the formylation of anisole (50% isolated yield) and alkylated benzenes in fair yield using acetone cyanohydrin (Eq 1.19). Similar to the Gattermann reaction no formylation is obtained with pyrrole and only traces of aldehydes were observed with phenol and furane as substrates. 

Azido esters such as 10 are readily prepared from the corresponding aldehyde by phos-phonate condensation. Shunsuke Chiba and Koichi Narasaka of Nanyang Technology University demonstrated (Organic Lett. 2008, 10, 313) that thermal condensation of 10 with acetyl acetone 11 gave the pyrrole 12, while Cu catalyzed condensation with acetoac-etate 13 gave the complementary pyrrole 14. 

Pyridoxol hydrochloride. See Pyridoxine HCI Pyridylcarbinol 3-Pyridylcarbinol 3-Pyridylmethanol. See Pyridine-3-methanol Pyroacetic acid Pyroacetic ether. See Acetone Pyrobenzol Pyrobenzole. See Benzene Pyrocellulose. See Cellulose Pyrochol. See Desoxycholic acid Pyrodextrin. See Dextrin 2-Pyrol. See 2-Pyrrolidone Pyroligneus acid. See Acetic acid Pyromucic aldehyde. See Furfural Pyrophyllite. See Aluminum silicate Pyrosulfurous acid disodium salt. See Sodium metabisulfite Pyroxylic spirit. See Methyl alcohol m-Pyrrole. See N-Methyl-2-pyrrolidone 2-Pyrrolidinone a-Pyrrolidinone. See 2-Pyrrolidone 2-Pyrrolidinone, 1-dodecyl-. See Lauryl pyrrolidone 2-Pyrrolidinone, 1-ethenyl, hexadecyl homopolymer CAS 63231-81-2... 

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