Silver-Sensitive Enantioselectivity in Asymmetric Heck Reactions

Abstract

Amine- and pure Ag(I)-promoted asymmetric Heck ­cyclisations of 2-iodobut-2-enanilide 1 both gave the oxindole product (R)-(+)-2 in relatively low ee but the partial reduction of the silver salt promoted a substantially more stereocontrolled route to (S)-(-)-2 in a reaction in which the use of Strem Ag₃PO₄ gave the R-product and Aldrich Ag₃PO₄ gave the S-product.

Key words

palladium - silver - Heck reaction - asymmetric catalysis - ring closure

References and Notes

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• 18b

  Sellarajah, S.; Stephenson, G. R. unpublished work.

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  information available from www.reactarray.com.

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19

McDermott, M. C. PhD Thesis, University of East Anglia, UK, 2005, submitted.

21

McDermott, M. C.; Stephenson, G. R.; Walkington, A. J. in preparation.

23

Samples taken by the SK233 were analysed using an Agilent 1100 series system equipped with a 50 mm × 2 mm Phenomenex Luna 3µ C18 (2) column and run at 220 nm using a H₂O to H₂O-MeCN (1:19) eluent, with the ratio of substrate to product peaks calibrated using an equimolar solution.

24

Results obtained from chiral analysis using a Chiracel OJ column eluted with hexane-EtOH 99.5:0.5 were calibrated by comparison to chiral shift experiments for a series of references samples. The ee are generally reproducible within a ±2% error range.

25

Relative nominal purities: Strem Ag₃PO₄ (99+%); Aldrich Ag₃PO₄ (98%).