Dihydrooxazine Oxides as Key Intermediates in Organocatalytic Michael Additions of Aldehydes to Nitroalkenes
作者:Gokarneswar Sahoo、Hasibur Rahaman、Ádám Madarász、Imre Pápai、Mikko Melarto、Arto Valkonen、Petri M. Pihko
DOI:10.1002/anie.201204833
日期:2012.12.21
Pause and play: Dihydrooxazineoxides are stable intermediates that are protonated directly, without the intermediacy of the zwitterions, in organocatalyticMichaeladditions of aldehydes and nitroalkenes (see scheme, R=alkyl). Protonation of these species explains both the role of the acid co‐catalyst in these reactions, and the observed stereochemistry when the reaction is conducted with α‐alkylnitroalkenes
Stoichiometric Reactions of Enamines Derived from Diphenylprolinol Silyl Ethers with Nitro Olefins and Lessons for the Corresponding Organocatalytic Conversions - a Survey
nitro‐ethenes), and nitro enamines derived from γ‐nitro aldehydes (6, often formed after longer reaction times). The same types of products were shown to be formed, when the reactions were carried out with peptides H‐Pro‐Pro‐Xaa‐OMe that lack an acidic H‐atom. Functionalized components such as alkoxy enamines, nitro‐acrylates, acetamido‐nitro‐ethylene, or hydroxylated nitro olefins also form products carrying