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Chapter 35 Suggested solutions for Chapter 35 303 Problem 6 Revision elements. Suggest two syntheses of this spirocyclic ketone from the starting materials shown. Neither starting material is available. 0 0 CHO ? ? ? ? pose of the problem of synthesis (Chapters 25 and 30) with some cycloaddition. Helping you to realize that are alternative ways to make six-membered rings. solution most obvious disconnection is of the ketone with an aldol reaction (Chapter 27) This reveals a 1,4-dicarbonyl compound. Direct disconnection to one of the starting materials possible and suggests a Diels-Alder reaction. o 0 4 0 CHO 1 CHO Diels- enone 3 2 CHO Alder CI + aldol The Diels-Alder reaction has the right ('para') regioselectivity, especially if we use a Lewis acid SnCl₄, and we shall need a nonbasic specific enol equivalent for the alkylation - an enamine fine. 0 R₂N CHO CHO 0 CHO CI heat R₂NH base TM Lewis acid The other route demands a different disconnection of the keto-aldehyde plus one further aldol The starting material is more easily made by Birch reduction than by a Diels-Alder o 4 1 0 OMe 3 CHO Birch 2 enone reduction aldol The Birch reduction gives the enol ether of the ketone and demands careful hydrolysis to avoid double bond moving into conjugation with the carbonyl group. The aldol reaction requires kind of control; perhaps the silyl enol ether of acetone will do. Then we need a reagent for

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