Consider these steps from the recent literature and answer the questions that follow.

i. Briefly explain what is happening at each step (i)–(iv). 2 marks 

ii. By considering the acetate (CH3CO), tert-butyldimethylsilyl (TBDMS) and benzyl (Bn or PhCH2) groups used in this example, explain what is meant by an orthogonal protecting group strategy. 2 marks 

iii. Propose a mechanism for the transesterification reaction occurring in step (ii). 2 marks 

iv. Outline a mechanism to show how dimethylsulfoxide (DMSO) and oxalyl chloride can combine to generate an activated sulfur-centred electrophile, while liberating CO2, CO and chloride ion (the first stage of step (v)). 3 marks

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i. TBDMSCI, Et,N HO Но. COTBDMS ii. KCO3, CH;OH 8 iii. BNCI, Et,N iv. TBAF v. DMSO, (COCI)2, EtN TBDMS = tert-butyl-dimethylsilyl TBAF = tetra-n-butylammonium fluoride BnCI = CI DMSO = dimethylsulfoxide 10 H i. TBDMSCI, Et,N HO Но. COTBDMS ii. KCO3, CH;OH 8 iii. BNCI, Et,N iv. TBAF v. DMSO, (COCI)2, EtN TBDMS = tert-butyl-dimethylsilyl TBAF = tetra-n-butylammonium fluoride BnCI = CI DMSO = dimethylsulfoxide 10 H