Catalytic Asymmetric Cycloadditions of Silyl Nitronates Bearing α-Aryl Group
摘要:
1,3-Dipolar cycloadditions of 2-alkylacroleins or atropaldehyde with triisopropylsilyl nitronates bearing an alpha-ary] group produced 3-aryl-2-isoxazolines having a chiral quaternary center in up to 94% ee and up to 88% yield with the aid of Corey's oxazaborolidine catalyst. Specifically, the TIPS nitronate with an alpha-(p-methoxyphenyl) group gave mainly the 2-isoxazolines having an all-carbon quaternary center.
Nitroalkanes as Versatile Nucleophiles for Enzymatic Synthesis of Noncanonical Amino Acids
作者:David K. Romney、Nicholas S. Sarai、Frances H. Arnold
DOI:10.1021/acscatal.9b02089
日期:2019.9.6
bond-forming reactions often require nucleophilic carbon species rarely compatible with aqueousreactionmedia, thus restricting their appearance in biocatalysis. Here we report the use of nitroalkanes as a structurally versatile class of nucleophilic substrates for C–C bond formation catalyzed by variants of the β-subunit of tryptophan synthase (TrpB). The enzymes accept a wide range of nitroalkanes to form
Minimizing the Amount of Nitromethane in Palladium-Catalyzed Cross-Coupling with Aryl Halides
作者:Ryan R. Walvoord、Marisa C. Kozlowski
DOI:10.1021/jo401249y
日期:2013.9.6
A method for the formation of arylnitromethanes is described that employs readily available aryl halides or triflates and small amounts of nitromethane in a dioxane solvent, thereby reducing the hazards associated with this reagent. Specifically, 2-10 equiv (1-5% v/v) of nitromethane can be employed in comparison to prior work that used nitromethane as solvent (185 equiv). The present transformation provides high yields at relatively low temperatures and tolerates an array of functionality, including heterocycles and substantial steric encumbrance.