Review Problems of Illogical Two Group Disconnections | Designing Organic Syntheses by Stuart Warren

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In this video, we will explain Illogical Two-Group Disconnections. This is the series of videos on the book of Designing Organic Syntheses by Stuart Warren. This organic chemistry video tutorial focuses on Review Problems of Illogical Two-Group Disconnections

190. Review Problem 14: Cyclopentenones (e.g. TM 190) occur in nature and are important in prostaglandin synthesis. How would you make this one?

191. Analysis: Start with the α,β-unsaturated carbonyl:

Synthesis: Ketone A is just pinacolone, the product of the pinacol rearrangement (frames
154-5).

192. Review Problem 15: This triol (TM l92) can be taken as a 1,4- or a 1,5-dioxygenated
compound. In fact only one of these will work. Suggest a synthesis.

193. Analysis: We must go back to the corresponding tricarbonyl compound, writing CHO or CO2Et for CH2OH. Then we see that the 1,5-dicarbonyl relationship is no use as there isn't room for a double bond (e.g. 3-4) in the precursor we would have to write. We have to use the 1,4 relationships:

REVIEW SECTION. SYNTHESIS OF LACTONES

204. Review Problem 16: Design a synthesis for TM 204, an intermediate in Khorana's Coenzyme A Synthesis, J. Amer. Chem. Soc., 1961, 83, 663.

205. Analysis: First open the lactone to reveal the true target

Synthesis: A mild base must be used to avoid the Cannizzaro reaction. The hydroxy acid A cannot be isolated and cyclises spontaneously. (Fleming p.92).

THE 1,4-DIOXYGENATION PATTERN
1,4-DICARBONYL COMPOUNDS
γ-HYDROXY CARBONYL COMPOUNDS
OTHER ‘ILLOGICAL’ SYNTHONS
REVIEW PROBLEMS

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