An Unexpected Transannular [4+2] Cycloaddition during the Total Synthesis of (+)‐Norcembrene 5. Issue 14 (11th February 2020)

• Record Type: Journal Article
• Authors: Breunig, Michael; Yuan, Po; Gaich, Tanja
• Is Part Of: Angewandte Chemie international edition. Volume 59:Issue 14(2020)
• Page Start: 5521
• Page End: 5525
• Publication Date: 2020-02-11
• Subjects: Diels–Alder reaction -- ring-closing metathesis -- terpenoids -- total synthesis -- transannular cycloaddition; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201912613
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: We report a concise and versatile total synthesis of the diterpenoid (+)‐norcembrene 5 from simple building blocks. Ring‐closing metathesis and an auxiliary‐directed 1, 4‐addition are the key steps of our synthetic route. During the synthesis, an unprecedented, highly oxidized pentacyclic structural motif was established from a furanocembranoid through transannular [4+2] cycloaddition. Abstract : They may look alike… During studies toward the total synthesis of the norditerpene natural product norcembrene 5, one diastereomer of a key intermediate (α‐OAc at C13) underwent clean and spontaneous Diels–Alder cycloaddition at room temperature (see scheme). However, the corresponding β isomer did not undergo a Diels–Alder reaction, but was oxidized to the corresponding furanone, which was further transformed into norcembrene 5.