Several Diels-Alder adducts between benzoquinones and cyclopentadiene were reduced to the corresponding diols 7a-c and 11. Treatment of these diols with strong acid triggered a skeletal rearrangement reaction resulting in compounds 8a-c and 12 that contain a 4,8-methanoazulene substructure. In addition, a dyotropic-like rearrangement of the tetracyclic lactone 13 to the spiro-lactone 18 was observed. Five of the structures were supported by X-ray analysis.
S y n t h e s i s o f t h e A b y s s o m i c i n C o r e S t r u c t u r eAbstract: The core structure of abyssomicin C (1) containing an oxabicyclooctanone ring and a tetronate was prepared from the addition product of lithium ethyl propiolate and 4-tert-butyldimethylsilyloxycyclohexanone. Tetronate formation via addition of sodium methanolate followed by hydrolysis gave the hydroxy tetronic acid 27. The spiro compound 27 could be cyclized to the tricyclic tetronate 23 by a transannular Mitsunobu lactonization. Alternatively, 27 could be prepared from the cyanohydrin cis-19.
Bridged compoundsBridged compounds Q 0060 Acid-Induced Rearrangement Reactions of Reduced Benzoquinone Cyclopentadiene Cycloadducts. -In the presence of strong acids diols of type (IV) undergo skeletal rearrangement to bicyclo[3.2.1]octane ring systems present in several natural products. Interestingly, treatment of the tetracyclic lactone (IX) with BF 3 etherate results in further rearrangement to the spiro lactone (X). -(EIPERT, M.; MAICHLE-MOESSMER, C.; MAIER*, M. E.; J. Org. Chem. 67 (2002) 24, 8692-8695; Inst. Org. Chem., Eberhard-Karls-Univ., D-72076 Tuebingen, Germany; Eng.) -Jannicke 18-066
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