Thiyl‐radical‐catalyzed cyclization reactions of N‐tosyl vinylaziridines and alkenes were developed as a new synthetic method for the generation of substituted pyrrolidines. The key to making this process accessible to a broad range of substrates is the use of a sterically demanding thiyl radical, which prevents the undesired degradation of the catalyst.
rate-determining C−C bond formation. The nucleophilic reactivities span over a range of 108 from the vinylethers 1a,x as the least reactivecompounds (comparable to allylsilanes) to the highly nucleophilic silyl ketene acetal 1u (comparable to enamines). Linear free enthalpy relationships are used to compare the reactivities of these compounds with those of other aliphatic and aromatic π-nucleophiles.
Double trouble: An efficient method for the preparation of two types of synthetically useful bicyclo[5.4.0]undecanes with an angular oxygen functionality was realized starting from easily available substrates; this method was based on the [3+2] cycloaddition reaction of the platinum‐containing carbonyl ylide (see scheme; R1=alkyl or alkoxy, R2=alkyl, R3=alkyl or vinyl).
双重麻烦:从容易获得的底物开始,实现了一种有效的方法,用于制备两种类型的具有角氧官能度的合成有用的双环[5.4.0]十一烷。此方法基于含铂的羰基内酯的[3 + 2]环加成反应(请参阅示意图; R 1 =烷基或烷氧基,R 2 =烷基,R 3 =烷基或乙烯基)。
Fragment-Based Reaction Discovery of Non-Ene-Type Carbon-Carbon Bond-Forming Reactions: Catalytic Asymmetric Oxetane Synthesis by Screening Olefinic Reactants without Allylic Hydrogen
作者:Koichi Mikami、Kohsuke Aikawa、Junpei Aida
DOI:10.1055/s-0031-1289540
日期:2011.11
Through fragment-based reaction discovery, catalytic asymmetric [2+2] cycloaddition was found to produce oxetanes from trifluoropyruvate and olefinic reactants without allylic hydrogen. This non-ene-type carbon-carbon bond-forming reaction smoothly proceeded under the influence of chiral Pd or Cu complexes as Lewis acid catalysts. The [2+2] cycloaddition afforded the oxetane derivatives in high yields and enantioselectivities even under 0.1 mol% catalyst loading and solvent-free conditions.
An organic thiyl radical catalyst for enantioselective cyclization
作者:Takuya Hashimoto、Yu Kawamata、Keiji Maruoka
DOI:10.1038/nchem.1998
日期:2014.8
A diverse array of chiral organocatalysts have been developed that rely on acidâbase interactions to promote enantioselective ionic reactions via the movement of electron pairs. The stereocontrol of radical reactions using organocatalysts is an alternative approach, and several studies have shown that synthetically useful reactivity can result by controlling the movement of single electrons. However, in these studies, it is still an acidâbased organocatalyst which forms a closed-shell intermediate with substrate prior to the radical reaction and imparts chiral information, and use of a chiral organic radical directly as catalyst has only rarely been explored. Here, we report the design of an organic thiyl radical catalyst with a carefully designed chiral pocket constructed around a chiral thiol precatalyst. The resulting catalyst was used to effect highly diastereo- and enantioselective CâC bond-forming radical cyclizations. The ability of thiyl radicals to promote reactions has been known for decades although its extension to asymmetric catalysis has only rarely been explored. Now, an organic thiyl radical catalyst with a carefully structured chiral pocket has been designed as a means to achieve highly enantioselective radical cyclizations.