An efficient synthesis of natural products using singlet oxygen
thesisposted on 29.01.2019, 12:07 by Yassir Al-Jawaheri
The treatment of 1,3-dienes with singlet oxygen to give endoperoxides represents a potent, chemo- and regioselective method for the introduction of oxygen functionality. Additionally, these endoperoxides products can be further utilized in the synthesis of added value compounds, as well as complex natural products. In the thesis a new method for the synthesis of acyclic 1,3-dienes is presented. Furthermore, both acyclic and cyclic 1,3-dienes are used in the synthesis of natural products using singlet oxygen (1O2) addition as a core strategy. A new approach for the synthesis of range of 1,3-dienes from aryl boronic acids and substituted propargyl alcohols via a palladium catalyzed has been developed. This reaction uses a base-free, Suzuki-Miyaura coupling followed by an unprecedented isomerization sequence and gives a wide range of cyclic and acyclic of 1,3- diene compounds with varying aryl groups in good isolated chemical yields. This reaction involves initial formation of an allene as intermediate which then undergoes ready rearrangement by way of a palladium hydride intermediate, which results from the interaction of palladium (0) and boric acid. To ascertain mechanistic conformation of this rearrangement the intermediary allenes were isolated and exposed to palladium (0) and boric acid. Additionally, direct injection ESI-MS was utilized to observe an intermediate palladium allyl complex; which can only occur form the addition of palladium-hydride to the allene. Furthermore, a range of stable allenes were then isomerized to 1,3-dienes by using the boric acid and a palladium (0) catalytic system. The synthetic utility of this reaction was applied by developing a convenient route to resveratrol from 1,3-diene. Additionally, we then utilized the addition of singlet oxygen to diene and were then able to convert the resultant endoperoxide to moracin M. Products Resveratrol and Moracin M Additionally, treatment of bicyclic 1,3-dienes with singlet oxygen to give bicyclic endoperoxides was examined as a method to deliver the core structure of the xanthanolide class of natural products. The xanthanolide skeleton, particularly xanthatin which is a potent anti-inflammatory natural product, contain a trans-fused ring system and can be obtained from the treatment of the endoperoxide with a malonate nucleophile via Korn Blum DeLaMare rearrangement. Significant progress toward the total synthesis of xanthatin was made, and we were able to obtain the advanced precursor, which is only 11-steps.
Iraq, Ministry of Higher Education.