New Multicomponent Reaction for the Direct Synthesis of β-Aryl-γ-nitroesters Promoted by Hydrotalcite-Derived Mixed Oxides as Heterogeneous Catalyst

D'Oca, Caroline R. M.; Naciuk, Fabricio F.; Silva, Jéssica C.; Guedes, Esthéfani P.; Moro, Celso C.; D'Oca, Marcelo G. M.; Santos, Leonardo S.; Natchigall, Fabiane M.; Russowsky, Dennis

doi:10.5935/0103-5053.20160175

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Articles • J. Braz. Chem. Soc. 28 (2) • Feb 2017 • https://doi.org/10.5935/0103-5053.20160175 copy

New Multicomponent Reaction for the Direct Synthesis of β-Aryl-γ-nitroesters Promoted by Hydrotalcite-Derived Mixed Oxides as Heterogeneous Catalyst

Authorship SCIMAGO INSTITUTIONS RANKINGS

A new approach based on multicomponent/domino combined reactions for the synthesis of γ-nitroesters promoted by a mixed aluminium-magnesium oxides derived from hydrotalcite-like material was developed. Different γ-nitroesters were synthesized in 15-95% yield using Meldrum's acid, aromatic aldehydes, nitromethane and different alcohols as reagents and solvents. The γ-aminobutyric acid derivatives, Phenibut and Baclofen, were prepared in 63 and 61% overall yield, respectively, through a two steps synthetic strategy. A mechanistic pathway was proposed based on the gas chromatography mass spectrometry (GC-MS) and electrospray ionization mass spectrometry (ESI-MS) experiments.

Keywords:
GABA; baclofen; mixed Al-Mg oxides; hydrotalcite; multicomponent; domino

entry	R¹	R²	Nitroester	Yield / %
1	C₆H₅	EtOH	5a	88
2	4-Cl-C₆H₄	EtOH	5b	83
3	4-Br-C₆H₄	EtOH	5c	88
4	4-F-C₆H₄	EtOH	5d	90
5	4-CN-C₆H₄	EtOH	5e	80
6	4-MeO-C₆H₄	EtOH	5f	70
7	3,4-(MeO)₂-C₆H₃	EtOH	5g	75
8	3,4,5-(MeO)₃-C₆H₂	EtOH	5h	95
9	2-thienyl	EtOH	5i	85
10	3-thienyl	EtOH	5j	83
11	nBu	EtOH	5k	15
12	iPr	EtOH	5l	17
13	C₆H₅	EtOH	5a	88^a a 1st recycle;
14	C₆H₅	EtOH	5a	85^b b 2nd recycle;
15	C₆H₅	EtOH	5a	70^c c 3rd recycle.

entry	R¹	R²	Nitroesters	Yield / %
1	C₆H₅	MeOH	5m	84
2	4-MeO-C₆H₄	MeOH	5n	72
3	C₆H₅	iPrOH	5o	75
4	4-MeO-C₆H₄	iPrOH	5p	64
5	4-MeO-C₆H₄	nBuOH	5q	55
6	C₆H₅	tBuOH	5r	58
7	C₆H₅	BnOH	5s	60^b b synthesized by the opening reaction of 6a.
8	C₆H₅	allyl	5t	75^b b synthesized by the opening reaction of 6a.
9	C₆H₅	propargyl	5u	65^b b synthesized by the opening reaction of 6a.

entry	Catalyst	Solvent	time / h	Temperature / ºC	Yield^a a Yields estimated by 1H NMR analysis; THF: tetrahydrofuran; DIPEA: N,N-diisopropylethylamine; DABCO: 1,4-diazabicyclo[2.2.2] octane; DBU: 1,8-diazabicyclo[5.4.0]undec-7-ene. / %
1	HT_[Calc.]	CH₂Cl₂	24	25	80
2	HT_[Calc.]	CH₃CN	24	25	61
3	HT_[Calc.]	THF	24	60	95
4	DIPEA	CH3CN	8	25	45
5	DIPEA	EtOH	8	25	67
6	DIPEA	EtOH	24	25	95
7	DIPEA	EtOH	8	reflux	95
8	DABCO	EtOH	5	60	95
9	DABCO	EtOH	3	reflux	95
10	DBU	EtOH	24	25	50
11	Et₃N	EtOH	24	25	95

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[1] *e-mail: dennis@iq.ufrgs.br