Trans- 1,4-acetoxylactonization

In a similar manner, the diacetates from cyclic dienes were enzymatically hydrolyzed and transformed to the enantiomers of diene acids 50 [71]. The diene acids from the seven-membered ring were subsequently used in intramolecular cis- and trans-1,4-acetoxylactonizations (cf. Scheme 8-14), leading to four different isomers of enantiomerically pure lactones. 

Intramolecular 1,4-Diacyloxylation An intramolecular variant of the palladiumutilizing dienes with a carboxyl group in the side chain (Scheme 11.16) [75, 76]. Also in this case the stereochemistry of the 1,4-addition can be controlled by variation of the ligand environment. Thus, in the absence of chloride a trans acetoxylactonization takes place, whereas in the presence of a catalytic amount of chloride a cis acetoxylactonization occurs. The catalytic intermediate was isolated and stereochemically assigned as its bipyridyl complex 49 [76]. In the stereochemical assignment, bipyridyl was utihzed... 

AcOH, followed by hydrolysis, gives the (/ )- , 3-dienecarboxylic acid 152. Then the acetoxylactone 153 can be prepared by the Pd-catalysed intramolecular trans-1,4-functionalization of the 1,3-cyclohexadiene 152. On the other hand, the acetate 155 is obtained by the Pd-catalysed chemoselective displacement of the allylic carbonate moiety in 154 with malonate under neutral conditions. The (5)-1,3-dienecarboxy 1ic acid 156 is obtained by Pd-catalysed 1,4-elimination of 155. The Pd-catalysed 1,4-functionalization of the 1,3-cyclohexadiene 156 and acetylation, afford 157, which is an enantiomer of 153 [101]. 

The palladium-catalyzed lactonization reaction has also been performed with hcxadicnyl acetic acids leading, under different reaction conditions, to either trans- or cis-acetoxylactonization products46. 

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