Development of Gold‐catalyzed [4+1] and [2+2+1]/[4+2] Annulations between Propiolate Derivatives and Isoxazoles

Abstract

Tw on ew gold-catalyzed annulations of isoxazoles with propiolates have been developed. Most isoxazoles follow an initial Oattackonthe alkyne to afforda[4+ +1] annulation product. This process results in ar emarkable alkyne cleavage of initial propiolates.U nsubstituted isoxazoles proceed through an Nattacks tep to yield formal [2+ +2+ +1]/[4+ +2] annulation products.T hese two annulation products arise initially from two seven-membered heterocyclic intermediates, which then lead to products.Supportinginformation for this article can be found under: http://dx.

Anthranils: versatile building blocks in the construction of C–N bonds and N-heterocycles

“…In addition, Liu and co-workers described an elegant goldcatalysed chemoselective annulation of electron-deficient alkynes 134 with anthranils to yield quinolone oxides (Scheme 50). 65 This annulation was compatible with substrates over a wide scope. It was found that the electron density of ligands has a significant impact on the chemoselectivity of this reaction.…”

Tandem Reactions of Ynones: via Conjugate Addition of Nitrogen‐, Carbon‐, Oxygen‐, Boron‐, Silicon‐, Phosphorus‐, and Sulfur‐Containing Nucleophiles

“…They have reported two kinds of annulations of isoxazoles with ynones to afford pyrroles 107.7 [Eq. (107‐1)] and imidazopyridines 107.8 [Eq.…”

“…(108‐2)]. It should be emphasized that an initial N‐attack of the 1,2‐benzisoxazole at the alkyne and an ester attack at the iminium moiety formed heterocyclic intermediates 108.1 and 108.7 , which are much different from those in the previous reaction . For species 108.5 , loss of the tert ‐butyl cation led to 108.11 [Eq.…”

BCl3-Mediated C–N, C–S, and C–O Bond Formation of Imidazo[1,2-a]pyridine Benzylic Ethers

“…1 Their analogues have been successfully used for pharmaceutical chemistry as well as in materials science. 2 Marketed drugs like alpidem, 3 zolpidem, 4 nicopidem and saripidem, 5 minodronic acid, 6 and optically active GSK812397 drug 7 are derived from the imidazo[1,2- a ]pyridine scaffold (Figure 1). 8…”