2.4- Pentadienoic acid, 5- -, ethyl

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). 

Similar carbocationic intermediates may be involved in the transformation of substituted ethyl pentadienoates under Ritter conditions in excess triflic acid (3 equiv.) to furnish the bicyclic aza compounds 163 [Eq. (5.254)].701... 

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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