The major product formed in the following reaction is

 

 

 

TBSOTf = t-Butyldimethylsilyl triflate

TBAF = tetra-n-butylammonium fluoride

Concept:

Conjugate addition:

• In conjugate addition reaction, a nucleophile reacts with an α,β-unsaturated carbonyl compound in the β- position. The negative charge carried by the nucleophile is now delocalized in the alkoxide anion and the α carbon carbanion by resonance.
• An example is shown below:

Wittig reaction:

• In the Wittig reaction, an aldehyde or a ketone is reacted with a triphenyl phosphonium ylide to yield an alkene along with triphenylphosphine oxide.
• An example is shown below:

Explanation:

• The reaction pathway is shown below:

• For the above reaction, we see that the PPh₃ (triphenylphosphine) and TBSOTf (tert-butyldimethylsilylester) undergo a conjugate addition reaction with the α,β-unsaturated carbonyl compound.
• The nBuLi (alkyl lithium reagent) abstracts a H atom from the intermediate product  and forms a triphenyl phosphonium ylide.
• The ylide reacts with butanal (Wittig reaction) to give the alkene along with triphenylphosphine oxide.
• In the last step, TBAF (Tetra-n-butylammonium fluoride) reacts with the tert-butyldimethylsilyl group and deprotects the alcohol group.

Conclusion:

Hence, the major product formed in the following reaction is 
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