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3. (6 points) The synthesis of cosalane, a new anti-HIV agent, has the following step: COOH COOH COOH HO ÇOOH сон H2SO4 HO HO OH CI 2 equiv 1 equiv Final Product Intermediate X (a) Draw an arrow-pushing mechanism for the formation of intermediate X. Show clearly how chemists rationalize the regioselectivity actually observed in the reaction. Resonance structures may help your argument. (b) Intermediate X is rapidly transformed under the reaction conditions to the final product. What is the structure of the Electrophilic reactive intermediate responsible for this rapid conversion?

Answer 1

WOH сори ann сон Intermediate Qo- on Step 1 - LE+ H + electrophile un from - - Mercrombie 604>enu (Regiculuckility is greened by this) и и ин nson) Shep D- 2004 - 40 con → Iron Yon a Sо и intermediate The reason for the pormation of product para toon group is that the ouho portions of the Eoor l-on) is blocked. Heve benune is unclergoung electrophilic auematic abstine tion rendhin which i favouri byelection donating substituint - among -01,-u {-401. The most activating group for europhilic wamatie substinskien is - on thewild then connes adually elichon windrauking CEWE)

K AN Page No. Date TTT Date coon -parato a a merato / This poution is favoured by all the three substitutente Para Ortho toon Reason & > Mability of the conjugati cow grained after the attack Of cluchephile governs the product. & as already stated elechon donating substituents faceren elechophilic aromatic substitution because it stabilites the caubecation intermediate an ortho 4 para portion → & elechon withdrawing substituente favour this reachionat mera poution became coobocation intermediate i destabilen at amod para position: 2 The below resonating structures give a better idea of this :- .-4. Con on & bo o n on on a 6004 Ulattack 100 Ato- E o E eu b poution cartoccation is shabilised by electronpairs of OH group i i atrack con on a lis attack on o l my e paraa pouilíon y be on doon on attack on mnia pentier hove positive charge ü located at smo & para loutions meanil mera periličn is tusceptible to attack bij electrophiles'

Page No. DateTT However, there is no direct stabilisation as is cose | 7 elechon donating groups Hesse elestron dénating groups ave moue powerful than wind rawing & electrophilia womatis substitution is dominated by or governed by theme ermediate This is the reason for the following produch regioselettivity no coon intermediate Lukimediaik rapidly concurkd Ź final product. yg electrophilic reachine linkrmediate CO04 coon 2004 2004 40 noon Ft Shipamson SD coon product