2-ethylidene-6-hepten-5-olide

Of these reactions perhaps the most important one is the telomerization of 1,3-butadiene with C02.91 The reaction is carried out under mild conditions (80°C, 40 bar total pressure) with a combination of [Pd(acac)2] (acac = acetylacetonate) and tertiary phosphines such as PPh3, PzPr3, or PCy3 as catalyst. This reaction can yield several products however, under optimal conditions the main product is the 8-lactone (2-ethyliden-6-hepten-5-olide) (Scheme 6.17). 

The reaction of C02 with 1,3-butadiene leads to the formation of 2-ethylidene-5-hepten-4-olide (126) in low yields (equation 157).587,588 Oligomers of butadiene are the major products. 

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