Diene coupling ester substituents

B.iv. Intramolecular Diene Coupling Influence of Ester Substituents... 

Trost et alJ2 also explored the compatibility of di-, tri-, and tetrasubstituted allenes with their intermolecular Alder-ene protocol. Multiple substituents present the opportunity for a mixture of products to arise from differing regio- and chemoselectivity. 1,1-Disubstituted allenes were coupled to methyl vinyl ketone with excellent chemo-selectivity only when one set of /3-hydrogens was activated by an cy-ester or amide (Equation (69)). If the /3-hydrogens were of similar acidity, a mixture of products was obtained, as in the coupling of allenol 103 with methyl vinyl ketone dienes 104 and 105 are produced in a 1.3 1 mixture (Equation (70)). 

In general, an ester (or a carboxylate) is borne by the alkyne 80 (except for nickel where a second olefin inserts and extends the metaUacycle) while the substituents on the olefin 81 vary a great deal, depending on the catalyst. Scheme 42 illustrates the synthetic utility of this coupling in the case of ruthenium catalysis [75]. Here, the dienes 82 are recovered regioselectively, the stereoselectivity depending on the olefin stracture. 

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