Copper(I)‐Catalyzed Highly Enantioselective [3+3]‐Cycloaddition of β‐Aryl/Alkyl Vinyl Diazoacetates with Nitrones

Abstract

Dedicated toProf. E. Peter Kündig on the occasion of his 75th birthday β-Aryl/alkyl vinyl diazoacetates were investigated in metallo-vinylcarbene reactions with nitrones, revealing a Rh 2 (OAc) 4 -catalyzed cyclopropene dimerization reaction and a copper(I) catalyzed [3 + 3]-cycloaddition of nitrones. The chiral cyclopropyl-In-SaBox ligand with copper(I) catalysis could realize the asymmetric version of the cycloaddition reaction, delivering various 3,6-dihydro-1,2-oxazine derivatives in good yield and with excellent enantioselectivity under mild conditions.

Photo-cycloaddition reactions of vinyldiazo compounds

“…Vinyldiazo compounds form either cyclopropenes (dinitrogen extrusion) 33 , 39 or 1 H -pyrazoles (cycloaddition/rearrangement) 34 , 36 . This dichotomy is found in the photochemical and thermal reactions of β-aryl-/alkyl-vinyl diazoacetates.…”

“…5C). For Ar and alkyl substituted nitrones, yields remained at the same level (25)(26)(27)(28)(29)(30)(31)(32)(33) while for glyoxalic acid derived nitrone reactions were less efficient (34,36). The yields, however, improved when deprotected oximidovinyldiazoacetate was used as a starting material, suggesting that the free hydroxyl group, by forming hydrogen bonds influences the reaction's efficacy (products 35, 37).…”

“…1A ). β-Aryl/alkyl vinyl diazocarbonyl compounds undergo non-reversible catalytic formation of unstable cyclopropenes via metallovinyl carbenes 34 , but thermally they form 3 H -pyrazoles that transform into 1 H -pyrazoles by 1,5-H transfer 35 . In particular, styryldiazoacetates undergo the thermal formation of 1 H -pyrazoles, but they do not form cyclopropenes in catalytic reactions 36 .…”

[3+3]-Annulation of Cyclic Nitronates with Vinyl Diazoacetates: Diastereoselective Synthesis of Partially Saturated [1,2]Oxazino[2,3-b][1,2]oxazines and Their Base-Promoted Ring Contraction to Pyrrolo[1,2-b][1,2]oxazine Derivatives

“…Based on the obtained and the literature [ 42 , 43 , 62 ] data, the following mechanism for the annulation was proposed ( Scheme 3 ). In the first step, electrophilic vinyl carbenoid species A is generated from vinyl diazo compound 2 and a rhodium catalyst.…”

“…Interestingly, the observed [3+3]-annulation with nitronates differs from the reaction of vinyl diazoacetates with nitrones, which often proceeds via a [3+2]-pathway and subsequent carbene reactions (cf. path b) [ 63 , 64 , 65 , 66 ], while the respective [3+3]-pathway was rarely observed [ 62 ].…”