Dolbier HW Solutions 400

Dolbier HW Solutions 400 - a , b-unsaturated ketone. A good...

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stereochemical integrity of the a carbon is lost. Reversion to ketone eventually leads to the formation of the more stable stereoisomer at equilibrium. The rate of enolization is increased by heating or by base catalysis. The cis ring fusion in the product is more stable than the trans because there are not enough atoms in the six-membered ring to span trans -1,2 positions in the four-membered ring without excessive strain. ( e ) Working backward from the product, we can see that the transformation involves two aldol condensations: one intermolecular and the other intramolecular. The f rst reaction is a mixed aldol condensation between the enolate of dibenzyl ketone and one of the carbonyl groups of the dione. This is followed by an intramolecular aldol condensation. ( f ) This is a fairly dif f cult problem because it is not obvious at the outset which of the two possible enolates of benzyl ethyl ketone undergoes conjugate addition to the
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Unformatted text preview: a , b-unsaturated ketone. A good idea here is to work backward from the f nal product in effect, do a ret-rosynthetic analysis. The f rst step is to recognize that the enone arises by dehydration of a b-hydroxy ketone. C 6 H 5 C 6 H 5 CH 3 C 6 H 5 O C 6 H 5 CH 3 C 6 H 5 O C 6 H 5 OH C 6 H 5 C CC 6 H 5 O O C 6 H 5 C CHC 6 H 5 C 2 2 H 2 O O C 6 H 5 C 6 H 5 C 6 H 5 OH C 6 H 5 O C 6 H 5 C 6 H 5 C 6 H 5 C 6 H 5 2,3,4,5-Tetraphenyl-cyclopentadienone 1 O O C 6 H 5 CCCH 2 C 6 H 5 C 6 H 5 CCC 6 H 5 O C 6 H 5 CH 2 CCH 2 C 6 H 5 Dibenzyl ketone C 6 H 5 CCC 6 H 5 O O Benzil O C 6 H 5 C 6 H 5 C 6 H 5 C 6 H 5 C 6 H 5 C CC 6 H 5 O O C 6 H 5 C CHC 6 H 5 C 2 C 6 H 5 CCC 6 H 5 O O O C 6 H 5 CHCCH 2 C 6 H 5 2 O H H Less stable ketone; starting material HO H Enol O H H More stable ketone; preferred at equilibrium CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 494 ENOLS AND ENOLATES...
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