In step (a), the hydrazone 8 reacts with 2 equivalents of butyl lithium (BuLi) to generate the anion 14. Propose a mechanism for this conversion. (4 marks)

TBSO OBn OTBS OTPS TPSO- a. n-BuLi, THE OBn NNHSO2A. H 10 TBSO TBSO TBSO OTPS OTPS OTPS c. LIAIH4, Et,0 OBn OBn OBn d. H. to 11 13 12 TPS = tert-butyldiphenylsilyl (-Si((C6H5)2C(CH3)3)) TBS = tert-butyldimethylsilyl (-Si((CH3)2C(CH3)3)) Bn = benzyl (CH2PH) acac = acetylacetonato (CH3COCH2COCH3) BuLi = butyl lithium (CH3CH2CH2CH2LI) b. .....