Q34E - Organic Chemistry (Mcmurry)

Question

The trimethylsilyl (TMS) protecting group is one of several silicon protecting groups for alcohols. For each reaction, draw the mechanism for the protection of (R)-3-bromo-1-butanol with the following silyl chlorides, using triethylamine as the base: 

(a) tert-butyldimethylsilyl chloride (TBS-Cl) 

(b) triisopropylsilyl chloride (TIPS-Cl) 

 (c) triethylsilyl chloride (TES-Cl)

Step-by-Step Solution

Answer

(a)

(b)

(c) 

Step 1: TMS protecting group

Trimethylsilyl is the protecting group used to block the interfering reaction which leads to the formation of the desired product after that deprotection is occurs so that we can again use the protecting group in the reaction.

Step2: Protection of 3-bromo,1-butanol with TBS-Cl

Alcohol protection on reaction with tert-dimethylsilyl chloride leads to the formation of tert dimethylsilyl ether by the removal of chloride and the reaction is proceed in presence of base triethylamine to form alkoxide from alcohol.

The reaction because silicon is the third-row atom and even larger than the carbon and forms a long bond due to which less hindrance occurs.

                                         Formation of Compound A

Step 3: Protection of 3-Bromo,1-butanol with TES-Cl

1. Alcohol protection on reaction with Tri ethyl silyl chloride lead to the formation of tri ethyl silyl ether by the removal of chloride 
2. Reaction is proceed in presence of base triethylamine to form alkoxide from alcohol.

                                         Formation of Compound B

Step 4: Protection of 3-bromo-1-butanol with TIPS-Cl

Alcohol protection on reaction with Tri isopropyl silyl chloride lead to the formation of tri isopropyl silyl ether by the removal of chloride and reaction is proceed in presence of base triethyl amine to form alkoxide from alcohol as shown below:

                          

                                   Formation of Compound C