A Convenient Access to Variously Substituted Spiro[cyclopropane‐1,4′‐oxazoline]s

Michael additions of carboxamides 2a – d under basic conditions onto methyl 2‐chloro‐2‐cyclopropylideneacetate ( 1 ) with subsequent ring closure furnished the 4‐spirocyclopropanated methyl oxazolinecarboxylates 3a – d (51–81 % yields), from which the corresponding free carboxylic acids 4a – d were obtained by hydrolysis in excellent yield (89–93 %). Coupling reactions of 4a – d with different o ‐hydroxyaniline derivatives in the presence of HOAt/EDC and 2,4,6‐collidine gave the anilides 5 in good to very good yields (55–92 %). The latter under Mitsunobu reaction conditions (Ph 3 P/DEAD) furnished the benzoxazole derivatives 6 (81–88 %). The bromine substituent in the N ‐methylated 4‐spirocyclopropanated 2‐(bromophenyl)oxazoline‐5‐carboxanilides 8c , d were aminated with various secondary amines under Buchwald–Hartwig reaction conditions to give the 2‐(aminophenyl)oxazolinecarboxanilides 9 (12–90 %). Suzuki cross‐couplings of 8c with arene‐ and hetareneboronic acids provided theoxazolines with 2‐biaryl substituents 10 – 13 (65–90 %). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)