A Straightforward Synthesis of Enantiopure (1<i>S</i>,2<i>R</i>)-Ephenamine

Velho, Arthur C. C.; Martins, José E. D.

doi:10.21577/0103-5053.20200121

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Article • J. Braz. Chem. Soc. 31 (12) • Dec 2020 • https://doi.org/10.21577/0103-5053.20200121 linkcopy

A Straightforward Synthesis of Enantiopure (1S,2R)-Ephenamine

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Abstract

An enantioselective six-step synthesis of (1S,2R)-ephenamine starting from readily available chiral amino acid is disclosed presenting 26% overall yield and high optical purity. The use of chiral phenylglycine as starting material was also studied and did not present satisfactory results due to a very sensitive a-carbonyl/benzylic stereogenic center that, in our hands, led to racemization.

Keywords:
chiral auxiliary; chiral amino alcohols; (1S,2R)-ephenamine


entry	Reagent (equiv.)	Solvent	Temperature / °C	time / h	Yield / %	anti/syna
1	NaBH₄ (3.0)	MeOH	-40	6	86	3.0/1
2	NaBH₄ (3.0)	EtOH	-78	4	95	1.1/1
3	NaBH₄ (3.0)	MeOH	rt	16	90	1/1
4	Zn(BH₄)₂ (2.0)	THF	-78	6	88	1.2/1
5	L-selectride (2.0)	THF	-78	6	90	1/1.6
6	LiAlH(OtBu)₃ (2.0)	THF	-78	4	90	1.1/1
7	DIBAL-H (2.0)	THF	-78	4	92	1/1

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[TFN1] ^a
The ratio was determined by ¹H NMR spectra from 1,2-amino alcohol obtained through Boc deprotection of 11. THF: tetrahydrofuran; DIBAL-H: diisobutylaluminium hydride; rt: room temperature.