Preparation of bridged bicycloalkanes via intramolecular [2+2] cycloadditions of ketenes a short total synthesis of (±)-clovene.

✍ Scribed by Raymond L. Funk; Perry M. Novak; Matthew M. Abelman

• Book ID: 104216518
• Publisher: Elsevier Science
• Year: 1988
• Tongue: French
• Weight: 240 KB
• Volume: 29
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)80333-0

✦ Synopsis

The preparation of a bridged bicyloalkane via an intramolecular ketene-olefm cycloaddition reaction in the context of a total synthesis of clovene is described.

The synthetic potential of the intramolecular ketene-olefm cycloaddition reaction is now widely appreciated.2 This method has been primarily directed toward the construction of fused polycarbocycles, eg. 1 -B 2 (Scheme I).

However, when the olefm and ketene are separated by a 3 or 4 carbon tether and the terminal carbon of the olefin is disubstituted, bridged bicy&c adducts are favored via a regioisomeric head to tail type of cycloaddition, cf. 3 -4.2b,c*g**n As a result of our experience with the intramolecular cycloaddition reactions of exocyclic &ones 5 to afford bridged bicycloalkanes of the general structure 6.3 we became intasted in the analogous ketene Scheme I olefin cycloaddition (7 * 8) which would produce the head to head bridged tricarbocyclic adducts 8. Herein, we document the feasibility of the cyclization process in the context of a total synthesis of (f)-clovene (11): an acid-catalysed rearrangement product of caryophyllene.5