Synthesis and Photochemistry of 5,5‐Dimethyl‐1H‐pyrrol‐2(5H)‐one and of Some N‐Substituted Derivatives

Abstract

In two steps, 5,5‐dimethyl‐1H‐pyrrol‐2(5H)‐one (3a) was prepared from 5,5‐dimethylpyrrolidine‐2,4‐dione ( = dimethyltetramic acid; 4) in 71% overall yield (Scheme 1) and further converted to N‐substituted derivatives 3b–f via acylation, alkylation, or methoxycarbonylation of its anion (Scheme 2). The substituents on the N‐atom exert a strong influence on the photochemical reactivity ([2 + 2] photocycloaddition to 2,3‐dimethylbut‐2‐ene, photocyclodimerisation, photoreduction) of these aza‐enones 3 (Scheme 3). In general, N‐alkyl compounds react much slower and with less efficiency than either the (N‐unsubstituted) title compound 3a or its N‐acetyl and N‐(methoxycarbonyl) derivatives 3e and 3f, respectively. These compounds behave similarly to the corresponding lactone, 5,5‐dimethyl‐2(5H)‐furanone, studied previously.

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

“…Initial work on the intermolecular [2 + 2] photocycloaddition of α,β-unsaturated γ-lactams was performed by Meyers and Fleming in the context of a synthetic approach to (−)-grandisol . Margaretha and co-workers studied the intermolecular [2 + 2] photocycloaddition chemistry of an N -unprotected γ-lactam, 5,5-dimethyl-l H -pyrrol-2­(5 H )-one, and of its N -acyl derivatives. , In later work, the Ohfune group found a high facial diastereoselectivity in the [2 + 2] photocycloaddition reactions of chiral N -Boc protected pyrrol-2­(5 H )-ones such as 385 (Scheme ). Cyclic stereocontrol guides the attack of ethylene to the more accessible bottom face of the molecule, and the formation of diastereoisomer 386 was preferred over 387 .…”

1,3-Bis(2,5-dihydro-5,5-dimethyl-2-oxo-1-pyrrolyl)-2,2-dimethyl-1,3-propanedione

“…The photochemical behavior of 2,5-dihydro-5,5-dimethylpyrrole-2-one (Ihlefeld & Margaretha, 1992) parallels that of the pyrimidine bases in DNA, e.g. uracil or thymine.…”

The 3,3,6,6-Tetramethylcis-transoid-cis-Photocyclodimer oftert-Butyl 2,5-Dihydro-5,5-dimethyl-2-oxo-1H-pyrrole-1-carboxylate

“…The photochemical behaviour of 5,5-dimethyl-lHpyrrol-2(5H)-one (Ihlefeld & Margaretha, 1992) parallels that of the pyrimidine bases of DNA, such as uracil or thymine. Direct irradiation (Ihlefeld & Margaretha, 1992) or hexadeuterioacetone-sensitized irradiation (Wrobel & Margaretha, 1997) affords a mixture of two dimers, (A) (major) and (B) (minor), whose structures were previously assigned on the basis of their I H NMR spectra only, because suitable single crystals could not be obtained. We have prepared the title compound, C22H34N206 (I), determined its structure by X-ray analysis, and then converted it to the major dimer (A), mentioned above, by double N-deprotection.…”