4.6- Retroretinoic acid

Aldol condensation of the retro Cj5 aldehyde (284) with ethyl senecioate (285) in the presence of potassium amide gave 4,6-retroretinoic acid (286). This compound reacted with methyl iodide to give the methyl ester, which was reduced with lithium aluminum hydride to 4,6-retroretinol (287) ( a-vitamin A ). Treatment of (287) with triphenylphosphine hydrochloride gave the C20 phos-phonium salt (288), while oxidation of (287) with manganese(IV) oxide produced the aldehyde (282) (Isler, 1971). 

D2 a-Retinoic acid [52978-64-0] 4,6-Retroretinoic acid a-Vitamin A acid 4,5-Didehydro-5,6-dihydro-retinoic acid... 

The prefix retro stated together with two positions of a retinoid structure indicates a shift in the conjugated polyene system. The first position gives the carbon atom from which a proton has been formally transferred to the carbon atom at the second position, e.g., 14-hydroxy-4,14-retroretinoic acid methyl ester (30) and 4,14-retroretinyl acetate (31). 

The acetylene carboxylic acid (273) underwent base-catalyzed isomerization to give 4,14-retroretinoic acid (137) in modest yield (Julia and Descoins, 1962), while the ether (274) was converted in the presence of sodium hydroxide to the conjugated 4,14-retroretinyl methyl ether (275) (Oroshnik et aL, 1952),... 

Didehydro-11,12-dihydroretinoids were synthesized by converting the Cjg ketone (421) by a Reformatsky reaction to the ester (422), from which the alcohol (423) was obtained by reduction with lithium aluminum hydride and the acid (424) by alkaline hydrolysis (Julia and Descoins, 1962). Compound (424) undergoes thermal isomerization to give 4,14-retroretinoic acid (137), and not... 

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