Serendipity at work: unexpected ring transformations of 4 aminopyrazolidin-3-ones into N-aminohydantoins

Abstract

Catalytic hydrogenation of (4R*,5R*)-4-benzyloxycarbonylamino-5-phenylpyrazolidin-3-one 2 in the presence of Pd-C furnished an unexpected 'ring switching' transformation product, 3-amino-5-benzylimidazolidine-2,4-dione 4. Furthermore, heating of azomethine imines 3a,b (derived from 2 and aromatic aldehydes) afforded the corresponding (Z)-5-benzylidene-3-[(E)-benzylideneamino]imidazolidine-2,4-diones 8a,b as ring transformation products. Both reactions are explainable by cleavage of the C(5)-N(1) single bond in substrates 2 and 3 followed by cyclocondensation of the amide nitrogen to the carbamate carbonyl group. The structure of hydantoin 8a was confirmed by X-ray diffraction.

Absolute Configuration Determination of 2,3-Dihydro-1H,5H-pyrazolo[1,2-a]pyrazoles Using Chiroptical Methods at Different Wavelengths

“…Later on, this would allow us to compare the influence of a given substituent on the specific rotation. Azomethine imines 1a – l with variable substituents at positions 4 and 5 and bearing typical aryl residues at position 1′ were prepared in good yields by condensation of racemic 3-pyrazolidinones 4a , 4b , 4c , 4d , and 4e and achiral compound 4f , with 5a – f following general literature procedures. ,, The Z configuration around the CN double bond in 3-oxopyrazolidin-1-ium-2-ides 1 and the trans configuration of 4,5-disubstituted pyrazolidinones 4a – c and dipoles 1 derived thereof were established previously. ,, Selected experimental data for dipoles 1a – l prepared from chemsets 4a – f and 5a – f are presented in Table .…”

“…Aromatic aldehehydes 5a – f , trifluoroacetic acid, CuI, and DIPEA are commercially available. Azomethine imines 1a – c , 1d , 1g , and 1l , tert -butyl ( S )-(3-oxopent-4-yn-2-yl)­carbamate ( 2 ), , 3-pyrazolidinones 4a , 4b , 4c , 4d , 4e , and 4f , and the nonracemic cycloadducts (+)- 3a – d and (−)- 3a – d were prepared following the literature procedures.…”

“…Compounds 1e , f , h – k were prepared following a general procedure for the synthesis of closely analogous compounds. , A mixture of pyrazolidinone 4 (1 mmol), aromatic aldehyde 5 (1.2 mmol), and anhydrous EtOH (4 mL) was stirred at rt for 5 min. Then, trifluoroacetic acid (2 drops) was added, and the mixture was stirred at rt for 12 h. The precipitate was collected by filtration and washed with EtOH and Et 2 O to give 1 .…”

Recent Advances in the Synthesis of Hydantoins: The State of the Art of a Valuable Scaffold

“…393 Abdul Nasser et al performed the synthesis of 3-[(2furylmethylene)-amino]hydantoin 394 The rearrangement of 4-aminopyrazolidin-3-ones into 3amino-hydantoins through catalytic hydrogenation reaction was also reported. 397 The authors assumed that hydrogenation would cleave at the same time the benzyl carbamate protecting group and the C-5-N-1 bond of the 4-aminopyrazolidin-3-one. The opened ring, under its carbamic acid form due to the presence of carbon dioxide, would cyclize again to afford the 3-aminohydantoin (Scheme 66).…”

A new synthesis of 3-arylideneamino- and 3-alkylideneamino-substituted hydantoins

“…Described syntheses of 3-aminohydantoin derivatives from acyclic precursors generally involve formation of one or two C-N bonds (e.g., N3-C4 [8,[12][13][14][15], C2-N3 [16][17][18], both N1-C2 and N3-C4 [19][20][21][22][23], both N1-C5 and N3-C4 bonds [24]). These compounds are also prepared using recyclizations of certain heterocyclic compounds [25][26][27][28][29][30][31][32][33]. It should be noted that there are only a few reports on the synthesis of N-alkylidene-and N-arylidene-3-aminohydantoins.…”