An improved method for the preparation of pyrrolidines by the cycloaddition of nonstabilized 2-azaallyl anions with alkenes

Preparation of Enantiopure Chiral Amino‐[D1]methyllithium Compounds and Determination of Their Micro‐ and Macroscopic Configurational Stabilities

“…DEAD (940 mg, 850 μL, 5.40 mmol) was added at 0 °C, and then the mixture was stirred at ambient temperature for 1 h. The reaction was quenched by adding a few drops of water, the solvent was removed under reduced pressure, and the residue was purified by flash chromatography (hexane/EtOAc 15:1; R f =0.33) to give 1.85 g (91 %) of 21 as a yellow oil. The spectroscopic data of the unlabeled compound were identical to those reported in the literature 44…”

Cycloadditions of Nonstabilized2-Azaallyllithiums (2-Azaallyl Anions) and Azomethine Ylides withAlkenes: [3+2] Approaches to Pyrrolidinesand Application to Alkaloid Total Synthesis

“…5 We have found that most of the cycloadditions of nonstabilized 2azaallyllithiums proceed with retention of the anionophile geometry, but we have found a few examples of non-stereospecific additions, again involving Z-stilbene (e.g. 29,36 Thus, while the geometry of Eand Z-alkenes is almost always conserved in cycloaddition reactions of nonstabilized 2-azaallyllithiums, the existence of stepwise examples may indicate that these reactions are borderline concerted, and may even be occurring by stepwise processes where ring-closure is faster than bond rotation. 29,36 Thus, while the geometry of Eand Z-alkenes is almost always conserved in cycloaddition reactions of nonstabilized 2-azaallyllithiums, the existence of stepwise examples may indicate that these reactions are borderline concerted, and may even be occurring by stepwise processes where ring-closure is faster than bond rotation.…”

“…29 This route was attractive because of the ready availability of the amines 59 using Chong and Park's methodology. alkylstannanes 59 were condensed with aldehydes or ketones, allowing the synthesis of (2-azaallyl)stannanes with up to three alkyl substituents (Scheme 15).…”

Vinyltrimethylsilane

“…18 Reaction of Vinyltrimethylsilane with 2-Azaallylanions. Reaction of vinyltrimethylsilane with the nonstabilized 2-azaallyl anion (19), generated in situ from the (2-azaallyl)stannane (18) (eq 10), produces, after quenching with MeI, the pyrrolidine (20) as a single diastereomer in 77% yield (eq 11). 21 Some evidence suggests that the cycloaddition is stepwise and that the 'W-conformation' of the anion predominates in the cycloaddition sequence.…”

“…Vinyltrimethylsilane reacts with chlorotriisopropoxytitanium in the presence of isopropylmagnesium chloride to form the interesting titanium(II) titanacycle (25) (eq 17), which reacts with esters to form β-trimethylsilylcyclopropanols (eq 18). These can be converted to the β-trimethylsilyl ketone (eq 19) Hydrogen Acceptor Catalyst in the Conversion of Alcohols to Hydrogenated Wittig Adducts. The ruthenium carbene catalyst (26) readily loses hydrogen to vinyltrimethylsilane to form the complex (27), which in turn readily accepts hydrogen from a primary alcohol reforming (26) and an aldehyde.…”