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(BQ) Part 2 book "Organic chemistry" has contents: Alkylation of enolates, the aldol and claisen reactions; sulfur, silicon and phosphorus in organic chemistry; saturated heterocycles and stereoelectronics; participation, rearrangement and fragmentation;.and other contents. | This page intentionally left blank Suggested solutions for Chapter 25 25 PROB LE M 1 Suggest how these compounds might be made by alkylation of an enol or enolate. EtO2C CO2Et O Purpose of the problem An exercise in choosing good routes to simple compounds. Suggested solution As you can see from the carbonyl groups in these compounds, it is pretty obvious which is the new bond to be made. In both cases, the electrophile will need to be an allylic halide. These are good electrophiles for SN2 reactions so they will work well here. We need to use the electrophile twice in the first case and the enolate is that of diethyl malonate. The second case will require an enol or enolate equivalent to prevent self-condensation: a silyl enol ether (p. 595 in the textbook) or an enamine (p. 591 in the textbook) is ideal. If you use a silyl enol ether, don’t forget the Lewis acid! EtO2C H EtO2C CO2Et 1. EtO H 2. CO2Et repeat EtO2C H Br Br Me3SiCl O Et3N + OSiMe3 SnCl4 or other Lewis acid O CO2Et The reason why allylic halides make good electrophiles is discussed in the textbook on p. 341. 250 Solutions Manual to accompany Organic Chemistry PROB LE M 2 How might these compounds be made using alkylation of an enol or enolate as one step in the synthesis? O O O O Purpose of the problem An exercise in using enolate chemistry to make carbonyl compounds disguised as acetals. Suggested solution See p. 227 of the textbook for a reminder of how to make cyclic acetals. The only functional group in either compound is an acetal. Cyclic acetals are made from diols and carbonyl compounds so we need to have a look at the deprotected molecules before taking any further decisions. H O O O OH OH H O HO O O HO If we are going to use enolate chemistry, we have to make the diols by reduction of carbonyl compounds. As both diols have a 1,3-relationship between the OH groups, the carbonyl precursors will be the very enolizable 1,3-dicarbonyl compounds, which can be
