2'-Hydroxyacetophenone → Benzyl 4-oxospiro[chroman-2,4'-piperidine]-1'-carboxylate

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Reaction Steps

The synthesis of compound 19A-19D is outlined in Scheme 19. The 2′-hydroxyacetophenone 1.1a was condensed with benzyl 4-oxopiperidine-1-carboxylate (19.1) in refluxing methanol in the presence of pyrrolidine to provide N-Cbz-spiro[2H-1-benzopyran-2,4′-piperidine]-4(3H)-one (19.2). Conversion of the ketone 19.2 to the enol triflate derivative 19.3 was achieved using N-phenylbis(trifluoromethanesulphonimide) 1.4 as triflating reagent. Conversion of the enol triflate 19.3 to the corresponding boron derivative 19.4 was achieved using 4,4,5,5-tetramethyl-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1,3,2-dioxaborolane 1.14 and dichloro[1,1′-bis(diphenylphosphino)ferrocene]palladium(II) dichloromethane adduct, abbreviated as [Pd(dppf)Cl2.CH2Cl2]. Suzuki type coupling of the boronate derivative 19.4 with tert-butyl 4-bromophenylcarbamate 19.5 in ethylene glycol dimethyl ether in the presence of tetrakis triphenylphosphine palladium(0), lithium chloride, and an aqueous solution of sodium carbonate afforded the tert-butyloxycarbonyl (Boc) protected aniline derivative 19.6. Acidic hydrolysis of 19.6 provided the aniline derivative 19.7 which reacted with acyl chlorides 19.8a, 19.8b, isopropylsulfonyl chloride (6.5b) or ethyl isocyanate (19.11) to give the corresponding amide derivatives 19.9, sulfonamide derivative 19.10 or urea derivative 19.12, respectively. The derivatives 19.9, 19.10 and 19.12 were converted to compounds 19A-19D by treatment with iodotrimethylsilane.

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