(b)You may recognize this compound as an enamine. It is slightly different, however, from theenamines we discussed earlier (Section 17.11) in that nitrogen bears a hydrogen substituent.Stable enamines are compounds of the typewhere neither R group is hydrogen; both R’s must be alkyl or aryl. Enamines that bear a hy-drogen substituent are converted to imines in a proton-transfer equilibrium.(c)The compound given is known as a nitronic acid;its more stable tautomeric form is anitroalkane.(d)The six-membered ring is aromatic in the tautomeric form derived from the compound given.(e)This compound is called isourea.Urea has a carbon–oxygen double bond and is more stable.18.37(a)This reaction is an intramolecular alkylation of a ketone. Although alkylation of a ketone with
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