1559T_ch25439-45310/20/055:59 AM Page445 EQA Solutions to Problems.445 attack by typical e ophiles.In this pa ular example, reaction at C2 gives a symmetrical intermediate with two equivalent resonance forms. E=CoHsN2" 35.(a b)Diels-Alder: 0 d)CH.CH-CH.CH-CC.Hs e CH、CH 6.(a)CH 女CH 00 (b)Hantzsch CoH CCHCOCH CH,HC-O.NH CH,CH,O0C、入 COOCHCH0 .C0.△ →product 入CH5 Rule out C4 (only two resonance forms for cation). Rule out C2 next, because attack results in an electron sextet and a positive charge on one of the electronegative N atoms. Thus, C5 is the site of attack by typical electrophiles. In this particular example, however, the major product is due to diazo coupling at C2, because under the basic conditions the imidazole anion is attacked, and reaction at C2 gives a symmetrical intermediate with two equivalent resonance forms. E  C6H5N2  35. (a) (b) Diels-Alder: (c) (d) (e) 36. (a) (b) Hantzsch product 1. HNO3, H2SO4 2. KOH, H2O 3. CaO, C6H5 C6H5 CH3CH2OOC COOCH2CH3 N H O O C6H5CCH2COCH2CH3 H2C O, NH3 O O CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 O P2O5, N C(CH3)3 CH3CH2CH2CH2CC6H5 O O C C6H5 S via N SH O O O O S O O O O S  N SO3H (CH3)2N N N  N N E E H   N N  E H  N N E H N H N Tautomerizes N N Product Solutions to Problems • 445 1559T_ch25_439-453 10/20/05 5:59 AM Page 445