Regioselectivity diene decarboxylative elimination

Decarboxylative elimination in 4-hydroxycyclohex-2-enecarboxylic acids with dimethylformamidedineopentylacetal has been shown to result in the formation of dienes in a regioselective manner under neutral conditions (equation 19)49. 

Pd-catalysed decarboxylation-elimination offers a useful method for regioselective generation of conjugated dienes. The polyene system of vitamin A derivative 381 is prepared from the /f-acetoxycarboxylic acid 379 by decarboxypalldation, as shown by 380 [172],... 

E. REGIOSELECTIVE FORMATION OF DIENES AND RELATED COMPOUNDS BY DECARBOXYLATIVE ELIMINATION... 

In fl-trimethylsilylcarboxylic acids the non-Kolbe electrolysis is favored as the carbocation is stabilized by the p-effect of the silyl group. Attack of methanol at the silyl group subsequently leads in a regioselective elimination to the double bond (Eq. 29) [307, 308]. This reaction has been used for the construction of 1,4-cyclohexa-dienes. At first Diels-Alder adducts are prepared from dienes and P-trimethylsilyl-acrylic acid as acetylene-equivalent, this is then followed by decarboxylation-desilyl-ation (Eq. 30) [308]. Some examples are summarized in Table 11, Nos. 12-13. 

---