Selected applications of N-protected (S)-2-(diazoacetyl)pyrrolidines (microreview)

N-Protected (S)-2-(diazoacetyl)pyrrolidines can be considered as a group of the N-protected (S)-proline derivatives. They can be conveniently prepared from the corresponding acyl chloride or mixed anhydride via Arndt–Eistert reaction.1 In recent years, the N-protected (S)-2-(diazoacetyl)-pyrrolidines have been widely explored as easily available, chiral building blocks bearing the reactive diazo function and have found numerous applications for the multistep synthesis of more complicated heterocycles including some natural products and their analogs. Some of them are reported to display biological activities, e.g., antifungal,2 α₄β₂ nicotinic acetylcholine receptor-binding,3 ^, 4 oxygen free radical scavenging,5 and selective antihistamine.6 Three types of key reactions performed with N-protected (S)-2-(diazoacetyl)pyrrolidines are a) halogenation via treatment with HX agents and N₂ elimination, b) catalytic decomposition and generation of reactive ketenes via the Wolff rearrangement of the intermediate α-oxo carbenes, and c) (3+2) cycloaddition reactions of the diazo 1,3-dipole with C=S dipolarophiles. In this article, mainly the papers from the period after 2001 are reviewed.