Department of Chemistry, Oakland University, 2200 N. Squirrel Road, Rochester, MI 48309-4477, USA.
School of Chemical Sciences, Dublin City University Glasnevin, Dublin 9, Ireland.
Chemistry. 2022 Apr 12;28(21):e202104391. doi: 10.1002/chem.202104391. Epub 2022 Mar 14.
A versatile asymmetric synthesis of bicyclic pyrazolidinones through alkaloid-catalyzed formal [3+2]- and [3+2+2]-cycloadditions of ketenes with azomethine imines is described. The methodology was found to be tolerant of ketene and a variety of monosubstituted ketenes (R=alkyl, OAc). The products were formed in good to excellent yields (71-99 % for 24 examples, 39 examples in all), with good to excellent diastereoselectivity in many cases (dr 3 : 1 to 27 : 1 for 22 examples), and with excellent enantioselectivity for most examples (≥93 % ee for 34 products). In the case of most disubstituted ketenes, the reaction proceeded through a [3+2+2]-cycloaddition to form structurally interesting bicyclic pyrazolo-oxadiazepinediones with moderate diastereoselectivity (dr up to 3.7 : 1) and as racemic mixtures (3 examples). The method represents the first unambiguous example of an enantioselective reaction between ketenes and a 1,3-dipole.
通过生物碱催化的偕二氟烯酮与亚胺叶立德的形式[3+2]-和[3+2+2]-环加成反应，实现了双环吡唑烷酮的多功能不对称合成。该方法对偕二氟烯酮和各种单取代的偕二氟烯酮（R=烷基，OAc）具有耐受性。产物以良好到优异的收率（24 个实例中为 71-99%，总共 39 个实例）形成，在许多情况下具有良好到优异的非对映选择性（22 个实例中 dr 为 3:1 至 27:1），并且对于大多数实例具有优异的对映选择性（34 种产物中的≥93%ee）。对于大多数二取代的偕二氟烯酮，反应通过[3+2+2]-环加成进行，形成具有中等非对映选择性（dr 高达 3.7:1）和外消旋混合物的结构有趣的双环吡唑并噁二嗪二酮（3 个实例）。该方法代表了偕二氟烯酮与 1,3-偶极子之间首次明确的对映选择性反应的例子。
