5-alkynylidene-l,3-dioxan-4-ones

Scheme 2.29 Diastereoselective 1,6-cuprate addition to chiral 5-alkynylidene-l, 3-dioxan-4-one 82.

By starting with enantiomerically enriched or pure j8-allenylcarboxylates, it is possible to carry out several of the transformations mentioned above stereoselectively. With regard to the required substrates, chiral 5-alkynylidene-l,3-dioxan-4-ones of... 

Diastereoselective 1,6-cuprate addition reactions to chiral dienones66 (Scheme 17) and acceptor-substituted enynes were reported recently. Due to an efficient shielding of the top face of the enyne moiety by the trifluoromethyl residue of the chiral 5-alkynylidene-l,3-dioxan-4-ones 115, the addition of lithium dimethylcuprate occurs preferentially at the underside to provide allene 116 with high diastereoselectivity after protonation with pivalic acid (Scheme 30).7,7a The stereochemical information generated in this step remained intact during the conversion into the chiral vinylallene 117. 

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