Chiral non-racemic N-cyanomethyloxazolidines: the pivotal system of the CN(R,S) method

Enantioselective Syntheses and Absolute Configuration of the Ladybird Defence Alkaloids (+)-Calvine and (+)-2-Epicalvine

“…Synthetic (ϩ)-1a {[α] D 20 ϭ ϩ18 (c ϭ 0.66, CH 2 Cl 2 )}, and (ϩ)-1b {[α] D 20 ϭ ϩ8 (c ϭ 0.58, CH 2 Cl 2 )}, exhibited spectral data ( 1 H NMR and MS) and capillary GC retention times identical to those of the corresponding natural and synthetic racemic compounds. [6] In order to determine the absolute configuration of natural calvine and 2-epicalvine, the mixture arising from another hydroxyethylation reaction of (2S,6S)-9a and (2R,6S)-9b was benzoylated with benzoic anhydride in the presence Next, we compared this synthetic route with an alternative one based only on the CN(R,S) method [9,10] (route B). To this end, compound (5S)-3 was subjected to a stereoselective decyanation [15] by sodium in liquid ammonia.…”

“…Our first approach used a combination of electrochemical [7,8] and CN(R,S) [9,10] methods, while the second was based exclusively on the latter technique. The two strategies are shown retrosynthetically in Scheme 1.…”

Asymmetric Synthesis of (S)‐4‐Oxopipecolic Acid by a 3+3 Atom‐Unit Assembly Strategy

“…Differential nucleophile/electrophile activity on either side of a chiral nitrogen synthon Ϫ effectively a chiral azomethine ylide Ϫ required complementary reactivity for each of the α-carbon atoms of an acetone equivalent. Previous work from our laboratory on chiral nonracemic N-(cyanomethyl)oxazolidines [17] suggested that compound 2 would be a useful candidate for the former fragment, [18] while an enol ether of an α-haloacetone appeared to be a convenient synthetic equivalent of the latter fragment. Encouraged by some preliminary studies on the use of such reagents for entry to piperidine derivatives, [19Ϫ21] we undertook the asymmetric synthesis of (S)-4-oxopipecolic acid [(S)-1] according to this strategy.…”

Diastereoselective Synthesis of Hexahydropyrrolo[2,1‐b]oxazoles by a Rhodium‐Catalyzed Hydroformylation / Silica‐Promoted Deformylation Sequence

“…This property of oxazolidines has been successfully utilized for the synthesis of a variety of naturally occurring and synthetic pyrrolidine and piperidine derivatives. [6] Herein, we report the novel synthesis of hexahydropyrrolo[2,1-b]oxazoles 2 a-h. This reaction proceeds diastereoselectively through a unique hydroformylationdeformylation pathway, involving the formation of a 1,3-oxazetidinium intermediate by addition of a carbonyl group to the iminium cation originated from the {NÀCH 2 ÀO} fragment of the oxazolidine heterocycle.…”