Allenyl Enolates – A New Class of Chiral Ambident Nucleophiles, 5. Ireland–Claisen Rearrangements of Allenic Silyl Ketene Acetals

Allenic silyl ketene acetals 3 formed by conjugate 1,6-addition of organocuprates to 2-propen-1-yl and 2-buten-1-yl 2-en-4-ynoates 1 and regioselective enolate capture with silyl electrophiles readily undergo [3,3]-Ireland-Claisen rearrangements to the 2-substituted methyl 3,4-dienoates 4. The simple diastereoselection of the formation of 4b could be improved by variation of the silylating agent as well as the addition of bases. in the case of product 4c, the sigmatropic rearrangement also takes place with good diastereofacial selectivity, i.e., with axis-to-center chirality transfer.

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