Enantio- and diastereoselective Darzens condensations

An Asymmetric Catalytic Darzens Reaction between Diazoacetamides and Aldehydes Generates cis‐Glycidic Amides with High Enantiomeric Purity

“…[6,7] Recently, North and co-workers reported an asymmetric Darzens reaction using a chiral cobalt complex as the catalyst, giving epoxy esters with moderate diastereoselectivity and enantioselectivity. [8] The catalytic asymmetric synthesis of trans-glycidic amides through chiral sulfur ylides, which are generated in situ from diazoacetamides and chiral binaphthylsulfide using a copper complex, provided a low yield and moderate enantioselectivity. [9a] Camphor-derived sulfonium amide could participate in a Darzens reaction with aldehydes to yield trans-glycidic amides with high enantioselectivity, although stoichiometric amounts of chiral sulfide was required.…”

“…By using readily available synthetic procedures, (2R,3R)-ethyl-3phenyloxiranyl carboxylate (5) could be converted into enantiomerically pure (2R,3S)-3-benzamido-2-hydroxy-3phenylpropanoic acid (7), [16] which is the side chain of taxol. Meanwhile, (2S,3S)-ethyl-3-benzyloxirane-2-carboxylate (6) served as a key synthetic intermediate for (À)-bestatin (8), which could be prepared according to an established procedure. [17] In conclusion, we have disclosed a highly diastereo-and enantioselective Darzens reaction of aldehydes with diazoacetamides catalyzed by a chiral titanium complex formed in situ from commercially available Ti(OiPr) 4 and (R)-binol, thus giving cis-glycidic amides with excellent enantiomeric purity.…”

The Fascinating Chemistry of α‐Haloamides

“…In addition to unsatisfactory diastereocontrol, the stereospecificity of the reaction was also scarce (up to 64 % ee for the major cis‐epoxides and up to 70 % ee for the minor trans‐epoxide). Three years later, results in step with the ones by Arai were reported by North and co‐workers which made use of a cobalt(salen) complex derived from ( R,R )‐diaminocyclohexane to catalyze the Darzens condensation reaction (Scheme ) …”

An Asymmetric Catalytic Darzens Reaction between Diazoacetamides and Aldehydes Generates cis‐Glycidic Amides with High Enantiomeric Purity

“…An asymmetric Darzens reaction with chiral phase transfer catalysts resulted in moderate enantioselectivity 6. 7 Recently, North and co‐workers reported an asymmetric Darzens reaction using a chiral cobalt complex as the catalyst, giving epoxy esters with moderate diastereoselectivity and enantioselectivity 8. The catalytic asymmetric synthesis of trans ‐glycidic amides through chiral sulfur ylides, which are generated in situ from diazoacetamides and chiral binaphthylsulfide using a copper complex, provided a low yield and moderate enantioselectivity 9a.…”