The influence of sidechain substituents in the intramolecular Diels-Alder reaction

The intramolecular Diels–Alder reaction: recent advances and synthetic applications

“…An alternative solution to the pestiferous cyclopentadiene rearrangement problem is to use a suitable blocking group, although chlorine was found to be unsatisfactory (198). This has been accomplished with a cyclopropane unit and 302 is employed in a recently completed total synthesis of the marine sesquiterpene sinularene (196). In similar fashion, an asymmetric total synthesis of longifolene is being developed from 303, in which the chiral cyclopropane centre directs the cyclization (197).…”

“…In principle, it should be possible to circumvent this difficulty by alteration of the carbonyl functionality (reduction, protection, etc.) but even this may fail, as in 522 (233), and the examples in 519 only cyclize when a homoallylic oxygen substituent is present (196).…”

“…Rearrangement of suitable intermediates was used for seychellene (208) and khusimone (199), while ring expansion of the Diels-Alder adducts afforded the required skeletons for cedrene, cedrol (186), and sativene (190). Cleavage of the cyclized intermediate for subsequent elaboraion is important in the preparation of sinularene (196), mansone E (231), resistomycin (273), farnesiferol C (239), karahana ether (237), and in approaches to gibberellic acid (232), longifolene (197), and capnellene (195). Useful variations on this cyclization-cleavage approach are those schemes in which extra rings are attached to the modified (cleaved) adduct, frequently by annulation, base catalyzed condensation, addition, or rearrangement reactions.…”

Studies of intramolecular Diels–Alder reactions: preparation of methyl spiro[2.4]hepta-4,6-dien-1-yl esters and their internal cycloaddition reactivity

“…Vinyl groups usually display a characteristic ABC pattern in their 'H nmr spectra at approximately 6 5 ppm. Although the appearance in this case was atypical (complex overlapping multiplet), the chemical shift was in the correct range, suggesting the structure was 5 rather than 4.3 Oxidation of 5 in dimethylsulfoxide containing di-'Please note that this assignment differs from our preliminary communication and that the substituents were attached incorrectly to C I I rather than Cz of the adducts (16 imparts. This was confirmed experimentally.…”

Addition initiated ring closure: synthesis of substituted spiro[2.4]hepta-4,6-dienes via cyclopentadiene intermediates from fulvene precursors

“…One solution we have developed is to block the rearrangement with a cyclopropyl unit which may serve as a source of latent functionality (6,7). In the course of these investigations we have devised a general route to spiro [2.4]hepta-4,6-dienes ("blocked cyclopentadienes") from fulvene intermediates via in situ generation of substituted cyclopentadiene anions.…”