Acid‐Catalyzed In Situ Generation of Less Accessible or Unprecedented N‐Boc Imines from N‐Boc Aminals

Recent Developments in the Stereoselective Synthesis of Nitrogen‐Containing Heterocycles using N‐Acylimines as Reactive Substrates

“…α,β‐Unsaturated aldehydes give satisfactory results in the synthesis of biscarbamates 4 , but modest yields are recorded in the formation of amido sulfones 5 because of a concomitant conjugate addition of the sulfinate anion . Propargyl aldehydes can be efficiently converted into alkoxy derivatives 3 , and biscarbamates 4 . Carboxylic acid amides, carbamates and substituted ureas can be profitably employed as nitrogen‐containing reactants leading to a diversified set of derivatives with peculiar electrophilic reactivities.…”

An Arylation Strategy to Propargylamines: Catalytic Asymmetric Friedel–Crafts‐type Arylation Reactions of C‐Alkynyl Imines

“…The classic strategy for preparing chiral propargylamines involves the asymmetric nucleophilic alkynylation of imines, thereby creating the chiral propargylic stereocenter in a C(sp)−C(sp 3 ) bond‐forming event (Scheme A) . Recently, several elegant asymmetric syntheses of propargylamines have been developed by utilizing electrophilic alkynyl imines that react with alkyl zinc reagents, silyl enol ethers, silyl ketene acetals,, enolizable aldehydes,– acetylacetone, β‐keto esters, malonate (thio)esters, and glycine Schiff bases as suitable nucleophiles; in these approaches, a C(sp 3 )−C(sp 3 ) bond formation is involved (Scheme B). However, to the best of our knowledge, chiral propargylamines still have not been synthesized in an arylation approach, which would involve a distinctive and complementary C(sp 2 )−C(sp 3 ) bond formation (Scheme C).…”

Organocatalytic Asymmetric Synthesis of Propargylamines with Two Adjacent Stereocenters: Mannich‐Type Reactions of In Situ Generated C‐Alkynyl Imines with β‐Keto Esters

“…[1] The standard method of preparing chiral propargylamines (1; Scheme 1) involves the asymmetric alkynylation of imines, thereby creating one new stereogenic center in the bond-forming reaction, [2] and a number of the catalytic variants of this transformation have also been reported (Scheme 1, path a). [4c] Accordingly, we were interested in the chiral phosphoric acid catalyzed reaction of in situ generated Calkynyl imines, [5,6] from the aminals 2, with b-keto esters as nucleophiles. [4c] Accordingly, we were interested in the chiral phosphoric acid catalyzed reaction of in situ generated Calkynyl imines, [5,6] from the aminals 2, with b-keto esters as nucleophiles.…”

“…[4c] Accordingly, we were interested in the chiral phosphoric acid catalyzed reaction of in situ generated Calkynyl imines, [5,6] from the aminals 2, with b-keto esters as nucleophiles. [7] The reaction between C-alkynyl imines and asubstituted b-keto esters would give polyfunctional chiral propargylamines having an alkynyl group and adjacent quaternary and tertiary stereocenters, [8,9] which cannot be prepared by the frequently employed alkynylation of imines.…”

“…[3] In contrast, there are only a few cases of the catalytic asymmetric addition of carbon nucleophiles (R 2 ) to C-alkynyl imines, thus giving chiral propargylamines (Scheme 1, path b), [4] and the reactions with prochiral nucleophiles to create two adjacent stereogenic centers are scarce, despite the high synthetic utility. [4c] Accordingly, we were interested in the chiral phosphoric acid catalyzed reaction of in situ generated Calkynyl imines, [5,6] from the aminals 2, with b-keto esters as nucleophiles. [7] The reaction between C-alkynyl imines and asubstituted b-keto esters would give polyfunctional chiral propargylamines having an alkynyl group and adjacent quaternary and tertiary stereocenters, [8,9] which cannot be prepared by the frequently employed alkynylation of imines.…”