I need the mechanism for the intermediate from A to B for the given drug

Antihistamines are taken to reduce the effects of allergic reactions in the body. The drug Fexofenadine is used to treat sneezing, runny nose and itchy eyes experienced by hay fever sufferers, without causing drowsiness. Fexofenadine is synthesized as shown below: intermediate A CH a C CH base CHN base CHN AC CHCINO NH PnMgBr intermediate E PMgBr CHNO then i OH OH Fexofenadine HC COH CMNO HO NaBH, Sto Ngy D CCINO