Optimization, mechanism, and kinetics of the hydrogenation of skipped polyynoic acids to all‐cis skipped polyenoic acids

Abstract

Hydrogenation of skipped polyynoic acids and esters over Lindlar's catalyst in the presence of quinoline proceeds with optimum results in light petroleum, ethyl acetate. or acetone at room temperature, yielding the corresponding all-cis polyenoic compounds in purities of 90-99%. depending on the number of triple bonds.For hydrogenations of this type mechanistic schemes are presented. including the formation of ene-ynoic intermediates. Using Langmuir adsorption and Hinshelwood kinetics. analogue computer simulation showed a simultaneous uptake of more than one H, molecule to be an important step in the reaction route.The formation of rrr1n.s-double bonds occurs only uirr isomerization of cisdouble bonds.In our laboratory the relationship between structure, essential fatty acid activity, and rate of conversion into prostaglandins of unsaturated fatty acids and the physiological action of the prostaglandins have been studied extensively (for a review see I ) . For this study. polyenoic acids and esters with 3 to 6 all-cis skipped double bonds had been prepared by cis-hydrogenation of synthesized polyynoic a c i d P 4 .Until now they were synthesized only by reduction in the presence of Lindlar's catalyst and quinoline5, followed by purification via T L C or counter-current distribution. Although &-hydrogenation of skipped

Are Alkyne Reductions Chemo-, Regio-, and Stereoselective Enough To Provide Pure (Z)-Olefins in Polyfunctionalized Bioactive Molecules?

“…The overall selectivity may be increased by addition of quinoline (0.05–1 molar equiv) to inhibit alkene surface interactions . This can be explained by morphological changes of the palladium particles.…”

“…As advised by Lindlar, quinoline is usually added into the reaction mixture . However, its quantity is often omitted .…”

Full Library of (Bis–allyl)‐deuterated Arachidonic Acids: Synthesis and Analytical Verification

“…The polyacetylene approach involves the assembly of C20 chain using iterative C‐alkylation of propargyl alcohol dianion with electrophilic propargyl bromide or tosylate . The resulting tetrayne product is then partially hydrogenated to tetraene and purified chromatographically . The latter approach provides a convenient way to the deuterated arachidonic acids, as it allows using D 2 ‐ propargyl alcohol instead of propargyl alcohol for creation of CD 2 ‐group in the bis ‐allylic position when needed.…”