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
1,2-Oxazine N-Oxides as Catalyst Resting States in Michael Additions of Aldehydes to Nitro Olefins Organocatalyzed by α,α-Diphenylprolinol Trimethylsilyl Ether
作者:Dieter Seebach、Xiaoyu Sun、Christof Sparr、Marc-Olivier Ebert、W. Bernd Schweizer、Albert K. Beck
DOI:10.1002/hlca.201200283
日期:2012.7
of the corresponding catalytic Michael‐addition cycles were formed and characterized (IR, NMR, X‐ray analysis; Schemes 3–6 and Fig. 1–3). Besides cyclobutanes 2, 1,2‐oxazine N‐oxide derivatives 3–6 and 8 have been identified for the first time, some of which are very stable compounds. It may not be a lack of reactivity (between the intermediate enamines and nitroolefins) that leads to failure of the