Photochemical Synthesis of N-Substituted 3-Hydroxy-2-pyrrolidinones

Abstract

A new three-step synthesis to 3-hydroxy-2-pyrrolidi­nones starting from β-amino acids has been developed. The key step is a novel reductive photocyclization.

Key words

3-hydroxy-2-pyrrolidinone - 4-hydroxypyroglutamic acid - α-keto ester - β-amino acid - reductive photocyclization

References

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6

General Irradiation Procedure.
The α-keto ester modified β-amino acids (2 or 4) were dissolved in 200 mL CH₂Cl₂ in a 250 mL pyrex flask. The solution was degassed with argon during 30 min and irradiated with a cooled 180 W mercury high-pressure lamp, which was immersed in the solution. After the photoreaction was finished the solvent was evaporated, and the residue purified by column chromatography yielding the pure 3-hydroxy-2-pyrrolidinones (3) or the 4-hydroxypyroglutamic acids (6).
Spectroscopic data for 3a as an example: ¹H NMR (400 MHz, CDCl₃): δ = 1.53 (s, 9 H), 1.96 (dtd, J = 12.4, 10.5, 9.1 Hz, 1 H), 2.44 (dddd, J = 12.4, 8.2, 6.6, 1.5 Hz, 1 H), 3.31 (br s, 1 H), 3.52 (ddd, J = 10.9, 10.5, 6.6 Hz, 1 H), 3.83 (ddd, J = 10.9, 9.1, 1.5 Hz, 1 H), 4.37 (dd, J = 10.5, 8.2 Hz, 1 H). ¹³C NMR (101 MHz, CDCl₃): δ = 27.1 (CH₂), 28.1 (CH₃), 42.2 (CH₂), 70.7 (CH), 83.6 (C), 149.9 (C), 174.8 (C). MS (ESI): m/z (%) = 425 (29) [2 M + Na]⁺, 224 (100) [M + Na]⁺, 168 (48) [M - t-Bu + Na]⁺.