An approach to 4‐hetarylisoxazole‐derived amines and other related 3,4‐disubstituted isoxazoles which relies on [3+2] cycloaddition of amino acid‐derived halogenoximes and push‐pull enamines is described. The target products are obtained at gram scale in up to 81 % overall yield. The efficiency of the method is affected by the electronic properties of the enamine component at the key step.
A scalable and efficient process for the preparation of 3-borylated pyrrolidines by 1,3-dipolar cycloaddition of Nbenzyl azomethine ylide generated in situ has been developed. The optimized method included the use of LiF in DMSO at 110 °C and was suitable for α-mono-, α,β-di-, and α,β,βtrialkyl-, β,β-(hetera)cycloalkylidene-, CO 2 Et-, as well as most β-(het)aryl-substituted alkenyl boropinacolates. The 1,3-dipolar reaction proceeded on a multigram scale providing 3borylated pyrrolidines with diverse substitution patterns (including fused and spirocyclic ones) in a diastereoselective manner. The Pd(OH) 2 -mediated N-debenzylation of pyrrolidine hydrochlorides was successfully performed to give the corresponding bifunctional building blocks on an up to 130 g scale, thus providing a substantial expansion of the synthetic and medicinal chemist's toolbox. Other reactions included the preparation of trifluoroborates, Zweifel-Aggarwal sp 3 -sp 2 coupling, and oxidative deborylation as an example of Cheteroatom bond formation.
The regioselective synthesis of 3,4- and 3,5-disubstituted izoxazole- and 1,2,4-oxadiazole-derived phosphonates is described, including analogues of phosphohistidine.
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