Preparation and Utility of Cyclic Enol Carbonates

Abstract

Treatment of iodo carbonates with LiHMDS at low temperature readily affords cyclic enol carbonates with either five- or six-membered rings. Reaction with potassium tert-butoxide results in the in situ formation of an enolate which after transmetallation participates in aldol or Mannich reactions. Alternatively, the potassium enolates can be trapped with silylating or triflating agents. The regio- and stereoselective generation of silyl enol ethers with up to four substituents can be achieved.

Key words

enols - aldol reactions - tandem reactions - stereoselectivity - regioselectivity

References

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11

Additional details for the preparation of substrates including isolation and characterization data are available upon request.

12

A procedure employing BuLi was also used extensively.

13

Due to inseparable mixtures and low diastereomeric ratios, full results are not reported at this time although representative procedures are provided.

15

Purified by flash chromatography utilizing an eluent that contained 0.5% Et₃N. Trimethylsilyl and triethylsilyl triflates gave products of low stability.