NOVELTY - Making efavirenz (IV) comprises: preparing 1-(2,5-dichlorophenyl)-2,2,2-trifluoro-ethanone (I) by reacting (2,5-dichlorophenyl)lithium (Ia) with e.g. trifluoro-acetyl chloride (Ic); preparing 5-cyclopropyl-2-(2,5-dichlorophenyl)-1,1,1-trifluoro-pent-4-yn-2-ol (II) by reacting (I) with a reagent-A; preparing ((1S)-4-cyclopropyl-1-(2,5-dichlorophenyl)-1-(trifluoromethyl)but-3-ynyl) carbamate (III) by e.g. reacting (II) with N-(oxomethylene)sulfamoyl chloride (IIIa); and preparing (IV) by intramolecular cyclization of (III).    USE - (IV) is useful for treating HIV infection. No biological data given.    ADVANTAGE - The simple method provides (IV) with improved yield and purity in an economical and environmentally friendly manner.    DETAILED DESCRIPTION - Preparing efavirenz (IV) comprises: preparing 1-(2,5-dichlorophenyl)-2,2,2-trifluoro-ethanone (I) comprising either reacting (2,5-dichlorophenyl)lithium (Ia) with a compound-A comprising trifluoro-acetic acid methyl ester (Ib), trifluoro-acetyl chloride (Ic) or (2,2,2-trifluoroacetyl) 2,2,2-trifluoroacetate (Id), or reacting 1,4-dichloro-benzene (Ie) with the compound-A in the presence of a compound-X, where compound-X is Friedel Crafts catalyst, and adding an acid; preparing 5-cyclopropyl-2-(2,5-dichlorophenyl)-1,1,1-trifluoro-pent-4-yn-2-ol (II) comprising reacting (I) with a reagent-A, where the reagent-A is obtainable from a reaction of a compound-B, a compound-C and a cyclopropane compound of formula (IIa), where the compound-B is achiral additive, the compound-C is compound-D, compound-E, compound-F, compound-G, compound-H, and/or compound-I, the compound-D is a (1-6C alkyl)2-zinc, the compound-E is a compound derived from cupper(I) or cupper(II), the compound-F is a compound derived from titanium(IV), the compound-G is an organolithium compound, the compound-H is a Grignard reagent, and the compound-I is zinc trifluoromethanesulfonate, tin(II) trifluoromethanesulfonate, indium(III) tribromide, trimethylaluminum, potassium tert-butoxide, zirconium isopropoxide, hydroxy(1,5-cyclooctadiene)rhodium(I) dimer, or tetrakis-(mu-acetato)dirhodium; preparing ((1S)-4-cyclopropyl-1-(2,5-dichlorophenyl)-1-(trifluoromethyl)but-3-ynyl) carbamate (III) comprising reacting (II) with N-(oxomethylene)sulfamoyl chloride (IIIa), and adding a base-A to the resulting reaction mixture, where the base-A is an amine compound of formula (N(R41)(R42)(R43)) (IIIb) and/or water; and preparing (IV) comprising intramolecular cyclization of (III) in the presence of a catalyst, a ligand and a base-B, where catalyst is compounds derived from cupper(0), cupper(I), cupper(II), palladium(0) and/or palladium(II), the ligand is diamine ligand, carbene ligand, phosphine ligand, phenanthroline ligand, hydroxyquinoline ligand, bis-imine ligand, bipyridine ligand, salicylamide ligand, pyrollidine ligand, glycine ligand, proline ligand, beta diketone ligand, sparteine ligand, and/or mono- or bidentate phosphor containing ligand, and the base-B is alkali phosphate, alkali hydrogen phosphate, alkali dihydrogen phosphate, alkali carbonate, alkali bicarbonate, alkali alcoholate, alkali hydroxide, alkyl amine, alkali hexamethyldisilazide and/or alkali amide.    M = H, Li, Na, K, Zn, Mg(X1), Cu(X1) or B(X1)2;    X1 = halo or CF3SO3; and    R41-R43 = H, phenyl or 1-10C alkyl.