2.4- Pentadienoic acid, 5- -, ethyl ester

A few drops of coned, sulfuric acid added to a mixture of ethyl acetoacetate and triethyl orthoformate, stored 24 hrs., and neutralized with a slight excess of quinoline ethyl j -ethoxy-cis-crotonate (Y 89%) dissolved in dry ether, added to a suspension of 2 moles LiNHg in anhydrous liq. NHg, stirring continued 10 min., a soln. of benzaldehyde in dry ether added, stirred 1 hr., NHg replaced by ether, refluxed 5 min., and ice-water added 3-ethoxy-5-phenyl-cis-2-frans-4-pentadienoic acid (Y 74%). — Excess LiNHg is used to prevent self-condensation of the ester. F. e. s. E. E. Smissman and A. N. Voldeng, J. Org. Ghem. 29, 3161 (1964). 

Posner and colleagues have recently made use of a [3,3]-sigmatropic rearrangement of an a,P-unsaturated sulfoxide as part of a regiospecific conversion of allylic alcohols into two-carbon-extended conjugated dienoate esters [233]. For example, reaction of allyl alcohol (291) with the sulfinyl orthoester (292) and a catalytic amount of 2,46-trimethylbenzoic acid in dichloromethane at 100°C produced ethyl pentadienoate (295) in 75% yield. The reaction is believed to... 

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