Diels-alder reaction of cinnamoyl dienophiles and terpene dienes and its application towards the synthesis of natural products / Thy Chun Keng

Thy , Chun Keng (2024) Diels-alder reaction of cinnamoyl dienophiles and terpene dienes and its application towards the synthesis of natural products / Thy Chun Keng. PhD thesis, Universiti Malaya.

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Abstract

The Lewis acid, AlBr3, was found to effectively catalyse the Diels-Alder reaction between cinnamoyl dienophile, trans-chalcone and terpene diene, (E)-ocimene to give the cycloadduct product of [(1RS,2SR,6RS)-3-methyl-2-(3-methylbut-2-en-1-yl)-6-phenylcyclohex-3-en-1-yl](phenyl)methanone in high yield (72%) and with excellent regio- (100:0) and diastereoselectivity (95:5). The effectiveness of the AlBr3 towards Diels-Alder reactions between various dienophiles and dienes was also evaluated. The acyclic dienes such as isoprene, 2,3-dimethylbutadiene and myrcene underwent Diels-Alder reaction with trans-chalcone, affording the corresponding adducts in relatively good yields (73-82%) and with excellent regioselectivity (90:10). A chiral titanium complex with 2 equivalents of FMOC-L-Phe-OH exhibited a significant enantioselectivity (61% ee) in the study of asymmetric Diels-Alder reaction of trans-chalcone and isoprene but unfortunately producing low yield (21%). A series of (±)-panduratin A derivatives were prepared by using AlBr3 as catalyst. Eighteen (±)-panduratin A derivatives were successfully synthesised with yields between 9 to 71%. The natural products, fislatifolione, isofislatifolione, fislatifolic acid, panduratins H and I were synthesised via thermal, catalyst and chiral complex-induced Diels-Alder reactions. The thermal-induced Diels-Alder reaction afforded the natural products in moderate yields (28-39%) and with moderate regioselectivities (67:33 to 77:23), but only fislatifolione and isofislatifolione were successfully synthesised through catalyst and chiral complex-induced Diels-Alder reactions.

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