Highly Diastereoselective Synthesis of N-Protected Arylglycine Derivatives
via TiCl ₄ -Promoted Friedel-Crafts Reaction of Phenols with Chiral N,O-Hemiacetal

Abstract

The optically active N-protected arylglycine derivatives were obtained via TiCl₄-promoted Friedel-Crafts reaction of various phenols with chiral N,O-hemiacetals in excellent diastereoselectivity.

Key words

Friedel-Crafts reaction - arylglycine - chiral N,O-hemiacetal

References

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22

The procedure for the synthesis of chiral N,O-hemiacetals 4a and 4b: 5 mmol of toluenesulfonamide was refluxed in EtOAc (35 mL) with 5mmol of (-)-8-phenyl menthyl glyoxylate ester hydrate and 10 mg of p-toluenesulfonic acid for two days to obtain 4a (major isomer) and 4b (minor isomer) of chiral N,O-hemiacetals 4 (1.6 g, 70% yield) respectively upon usual work-up and flash column chromatography on silica gel (EtOAc/petrol ether = 1:8).

23

The optical rotation of the recovered (-)-8-phenyl menthol was almost identical with that of literature: [α]_D -27 (ethanol, c 1.0), lit. [24] [α]_D -26.4 (ethanol, c 1.91).