Synthesis Of Carotenoids Based On Preparation Of α,β-Unsaturated Aldehyde With α-Tertiary Center

Carotenoids are a class of natural products commonly found in nature.More than850 kinds of carotenoids have been discovered by humans so far,such as lycopene（Ⅵ）,β-carotene and so on.Carotenoids are widely used in many fields such as food,cosmetic,feed and pharmaceuticals,and they have broad market prospects.The demand for carotenoids is constantly increasing in today’s society,and it is of great significance to research the efficient synthetic process.A method to prepareα,β-unsaturated aldehyde withα-tertiary center was used to synthesize lycopene（Ⅵ）.Firstly,Pseudoionone（Ⅰ）was adopted to synthesize 2,6,10-trimethylundeca-3,5,9-trienal（Ⅱ）.Then diethyl（3,7,11-trimethyldodeca-1,4,6,10-tetraenyl）phosphonate（Ⅳ）,was formed by Wittig-Horne reaction of the aldehyde II and tetraethyl methylenebis-phosphonate（Ⅲ）.The final product,all-E lycopene,can be collected after Wittig-Horner reaction and isomers rearrangement of compoundⅣand 2,7-dimethylocta-2,4,6-triene-1,8-dial（Ⅴ）.The synthesis of lycopene needed only 3 steps,with the yield of 37.0%.The structure of all-E lycopene was characterized by IR,HRMS and NMR techniques.The effects of the mole ratio of materials and reaction time on synthesis of intermediateⅡwere discussed when preparing all-E-lycopene.The optimum reaction conditions were determined as follows:n（Ⅰ）∶n（ICH₂Cl）∶n（TMSCH₂Li）∶n（Li Br）=1∶3∶3∶3 and the reaction time was 12 h.In addition,the effects of catalyst type,catalyst amount,reaction time,and reaction temperature on synthesis of productⅥwere discussed.The optimum reaction conditions were determined as follow:t-Bu OK as a basic catalyst,n（Ⅳ）∶n（t-Bu OK）=1∶1.2,reaction time was 3 h,and reaction temperature was 30℃.A key intermediate ofβ-carotene,2-methyl-4-（2,6,6-trimethylcyclohex-2-en-1-yl）but-2-enal,was also synthesized based on the preparation method ofα,β-unsaturated aldehyde withα-tertiary center strategy.The key intermediate ofβ-carotene was obtained fromβ-ionone as one step reaction,with the yield of 86.9%.The structure of the compound was initially characterized by GC-MS techniques.The effects of reaction temperature,mole ratio of materials and reaction time were discussed when preparing the key intermediate.The optimum reaction conditions were determined as follow:reaction temperature was 25℃,n（β-ionone）∶n（ICH₂Cl）∶n（TMSCH₂Li）∶n（Li Br）=1∶3∶3∶3 and the reaction time was 12 h.