Bisketene Equivalents as Diels–Alder Dienes

2,5-Bis­(tert-butyldimethyl­silyloxy)­furans
are established as vicinal bisketene equivalents for application as
dienes in the Diels–Alder reaction. Cycloaddition with olefinic
dienophiles, under exceptionally mild conditions, enables convergent
access to highly substituted para-hydroquinones in
unprotected form via a one-pot Diels–Alder/ring-opening/tautomerization
sequence. The synthesis of para-benzoquinones from
acetylenic dienophiles, including benzynes, is also demonstrated,
and 2,5-bis­(tert-butyl­dimethyl­silyloxy)­pyrroles
are established as competent dienes for the synthesis of para-iminoquinones. Application in natural product synthesis enables
gram-scale access to the neuroprotective agent (±)-indanostatin.

2,5-双(叔丁基二甲基硅氧基)呋喃（2,5-Bis(tert-butyldimethylsilyloxy)furans）已被确立为邻位双烯酮等价体，可作为双烯体（dienes）应用于狄尔斯-阿尔德反应（Diels–Alder reaction）。该类化合物与烯烃类亲双烯体（olefinic dienophiles）在极温和的反应条件下发生环加成反应，通过一锅法狄尔斯-阿尔德/开环/异构化序列，可直接获得未保护形式的高取代对苯二酚（para-hydroquinones），实现汇聚式构建。研究同时证实，以炔烃类亲双烯体（acetylenic dienophiles，包括苯炔（benzynes））为底物可合成对苯醌（para-benzoquinones）；此外，2,5-双(叔丁基二甲基硅氧基)吡咯（2,5-bis(tert-butyldimethylsilyloxy)pyrroles）可作为适用性良好的双烯体用于对亚胺醌（para-iminoquinones）的合成。将该策略应用于天然产物合成，可实现克级规模制备神经保护剂(±)-indanostatin。