Stereocontrol in cycloadditions of (1Z,4R*,5R*)-1-arylmethylidene-4-benzoylamino-5-phenylpyrazolidin-3-on-1-azomethine imines

Self Cite

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.

Section: Discussionmentioning

confidence: 99%

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

Novak¹,

Bezenšek²,

Grošelj³

et al. 2010

Self Cite

“…This has been previously shown by regio-and stereo-selective copper(I) iodidecatalyzed cycloadditions of ethyl propiolate in refluxing dichloromethane. 76 In contrast, the noncatalyzed cycloadditions required harsh thermal activation (~150 °C) and led to mixtures of isomeric cycloadducts. 77 In extension, an optimized Cu-catalyzed method that allowed the preparation of separable non-racemic products under mild conditions was developed.…”

Section: Page 189mentioning

confidence: 99%

“…81 Also here, the regioselectivity and stereoselectivity of the cycloadditions and relative configurations of cycloadducts were in agreement with previous results obtained by closely related cycloadditions (Scheme 18). 9,38,41,76 removal of the Boc group gave the 1-unsubstituted pyrazolidinones 72b-g in 77-99% yields. Subsequent hydrogenolysis of the Cbz group followed by cyclisation of the so-formed free 1,4-diamine with CDI, and chromatographic workup furnished title compounds 73b-h in 28-65% yields over the last two steps.…”

Section: Page 189mentioning

confidence: 99%

“…[40][41][42]44,47,[72][73][74][75][76][77] The 1 H-NMR spectroscopic data of the pyrazolidinones 4 and 25-33 and azomethine imines 24 revealed some interesting structural features of these compounds. In solution, these pyrazolidinone derivatives can equilibrate between two envelope conformers A and C via the planar conformer B (Scheme 21).…”

Section: Structural Features Of 3-pyrazolidinonesmentioning

confidence: 99%

See 1 more Smart Citation

Recent advances in the synthesis of polysubstituted 3-pyrazolidinones

Grošelj¹,

Svete²

2015

Self Cite

An account of recent developments in the field of 3-pyrazolidinone chemistry is given with special focus on the synthesis and transformations of 5-substituted 4-benzyloxycarbonylamino-3-pyrazolidinones, pyrazolo[1,2-a]pyrazole-based peptide analogues, and tetrahydropyrazolo-[1,5-c]pyrimidine-2,7-diones. In terms of practical application, polyfunctionalized 3-pyrazolidinones as 'aza-deoxa' analogues of cycloserine, peptide mimetics based on 3-amino-2-oxo-1,5-diazabicyclo[3.3.0]octane-7-carboxylic acid, and 1,6-disubstituted tetrahydropyrazolo[1,5-c]-pyrimidine-2,7-diones as the first representatives of a novel saturated heterocyclic system were prepared by these newly developed synthetic methods.

“…Surprisingly, recent NMR and X-ray structural determinations showed, that the configurations at positions 6, 7 and 9 were in agreement with the previously established stereocontrol, while the configurations at positions 3a and 9a were not. 51 This might be due to possible isomerisation at positions 3a and 9a…”

Section: Scheme 11mentioning

confidence: 99%

Utilisation of chiral enaminones and azomethine imines in the synthesis of functionalised pyrazoles

Svete¹

2005

Self Cite

Chiral enaminones, derived from commercially available enantipure starting materials, such as (+)-camphor and α-amino acids, were employed in cycloconcensation reactions with hydrazine derivatives to afford the corresponding pyrazoles, functionalised with terpene, alanine, 2-phenylethylamine, and β-amino alcohol moiety. On the other hand, recent study on stereocontrol in cycloadditions of racemic (1Z,4R*,5R*)-1-arylmethylidene-4-benzoylamino-5-phenylpyrazolidin-3-one-1-azomethine imines, available in three steps from hippuric acid, showed, that stereodirecting phenyl group, as well as ortho-substituents at the aromatic ring, control the selectivity of these cycloadditions. In extension, these results are now applied in a study, which is oriented towards combinatorial synthesis of pyrazolo[1,2-a]pyrazolone type of peptidomimetics with variable, yet predictable configuration.