The Stereoselective Synthesis of 2-Substituted 3-Azabicyclo[3.2.0]heptanes by Intramolecular [2+2]-Photocycloaddition Reactions
作者:Thorsten Bach、Christa Krüger、Klaus Harms
DOI:10.1055/s-2000-6261
日期:——
The stereoselective synthesis of the 3-azabicyclo[3.2.0]heptanes 6, 12, 13, 17, 22, 23 and 24 by an intramolecular [2+2]-photocycloaddition is described. The product yield was good to excellent in almost all cases studied (65-87%) except for a single example (21 → 24) in which a low yield was recorded (22%). The facial diastereoselectivity of the reaction is high if α-branched N,N-diallylamines are employed as starting materials which either bear a comparably bulky α-substituent (25) or the α-substituent of which is connected to the nitrogen atom via an oxazolidinone ring (16, 19, 20, 21). These diallylamines were readily prepared from methionine and it was shown that their preparation proceeded free of racemization. The photocycloaddition could be conducted in two ways. The more general method is based on the Cu-catalyzed reaction which was carried out with Cu(OTf)2 in diethyl ether and is applicable to essentially all substrates under scrutiny. The N-cinnamyl substituted substrates 5, 11, 16 and 25 which possess a comparably low lying T1 state reacted well in a triplet-sensitized process employing acetophenone as the sensitizer and acetone as the solvent.
本文描述了通过分子内[2+2]光环加成反应合成3-氮杂双环[3.2.0]庚烷6、12、13、17、22、23和24的手性选择性合成方法。在所有研究的情况中,产物收率良好至优异(65-87%),仅有一个例外(21→24)记录到较低的收率(22%)。如果使用α-支链的N,N-二烯丙基胺作为起始材料,这些材料要么带有相对较大的α-取代基(25),要么其α-取代基通过恶唑烷酮环与氮原子相连(16、19、20、21),反应的面选择性非常高。这些二烯丙基胺很容易从甲硫氨酸制备,并且证明其制备过程没有发生消旋化。光环加成反应可以通过两种方式进行。更通用的方法是基于铜催化的反应,使用Cu(OTf)2在二乙醚中进行,适用于几乎所有待研究的底物。拥有相对较低T1态的N-肉桂基取代底物5、11、16和25在三重态敏化过程中反应良好,使用乙酰苯作为敏化剂,丙酮作为溶剂。