Dimethyl octamethyltricyclo[4.2.2.02,5]deca-3,7,9-triene-7,8-dicarboxylate (Cookson's diester) revisited: Cope rearrangement and epoxidation site selectivity
✍ Scribed by Ronald N. Warrener; Gordon M. Elsey; Ian G. Pitt; Edward R.T. Tiekink; Richard A. Russell
- Publisher
- Elsevier Science
- Year
- 1994
- Tongue
- French
- Weight
- 321 KB
- Volume
- 35
- Category
- Article
- ISSN
- 0040-4039
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✦ Synopsis
A6s@m& Diiethyl octamethyltricyclo[4.2.2.~~5]d~&3,7.9-triene-7$dicarboxylate (Cookson's diester) (8) is reman@ tbmally via a double Cope reaction to its ring-degenerate isomer (14). The structme of dkter (3) (iodkactly) and the remangement product (14) (directly) Bn placed al M uneqaivocal base by X-Ray sIruc(uc analyxis. AM1 semiCnrpiricai catcuiatkms snpport the preferential fommtion of (8) fmm the restioa of DMAD with tmnsbt term&W diene (7). Epoxidatioa studier (mCPBA) have been cahcted and fim~ site se1ectivilie.s &tamincd. A The retro Diels-Alder reaction is a recognised protocol for the thermal generation of strained olefins.*s In particular, the ejection of the unsaturated species (3) from W-bridged benzenes (1) as outlined in Scheme 1 is especially facile as it is driven by the formation of an aromatic species (2) as co-product.lb Thus, in searchiig for a precur8or suitable for the thermal generation of Dewar furarts we were attracted to cyclobutene epoxides of type (4) as a possible substrate. For this reason we investigated the epoxidation of Cookson's diester (It) as a route to tetramethyl Dcwar fttran and this is the topic of the present communication.
, , Scheme 1: The retrodiene cleavage of 1,4-substituted benzenes as a thermal route to olqins Cookson's diester is prepared by heating dimethyl acetylenedicarboxylate (6) (DMAD) with tetramethylcyclobutadiene dimer (5) and the reaction is presumed to involve prior ring-opening of (5) to