The present invention provide process of preparation of (2R,3S)—N-carboxy-3-phenylisoserine, N-tert-butyl ester, 13-ester with 5(β)-20-epoxy-1,2(α),4,7(β),10(β),13(α)-hexa hydroxy tax-11-en-9-one 4-acetate 2-benzoate or docetaxel and its trihydrate (I)