i. Demonstrate your understanding of retrosynthetic analysis by redrawing step (i) in the retrosynthetic direction. Show the disconnection, retrosynthetic arrow, and synthons corresponding to the starting materials. 2 marks 

ii. Now redraw step (iii) in the retrosynthetic direction, showing disconnections and synthons corresponding to the starting materials. 3 marks 

iii. Consider the use of benzothioic S-acid 3 in this sequence. How many atoms are there in one molecule of this reagent? How many atoms does this reagent contribute to the structure of 7? Is this an atom efficient process? Why do you think this reagent is used? 3 marks

OEt SH Br i. KOtBu OEt ii. NaOH OEt Ph HS Et DMF THF/ H20 Et Et 3 4 6 benzothioic S-acid iii. TSOH Ph. PhMe, 120 C OEt Lamivudine 1 Ph S- 7 OtBu = tert-butoxide (-OC(CH3)3); Et = ethyl (-CH2CH3); DMF = dimethylformamide; Ph = phenyl (-CeHs); TSOH = p-toluenesulfonic acid; THF = tetrahydrofuran; PhMe = toluene