On the origin of some cubebene derivatives — Diels–Alder adducts and the diene structures of solidago compounds

Abstract

Two reactions, HCl addition and the thermal and (or) microwave assisted Diels-Alder condensation, were performed on α-cubebene (1), a vinylcyclopropane-containing tricyclic sesquiterpene. The diene structures originating from these reactions and from subsequent rearrangements of 1 were identified. The stereochemistry of the resulting adducts was established using mostly 2D high-resolution NMR.

Natural sesquiterpenoids

“…163 Two reactions, the HCl addition and the thermally or microwaveassisted Diels-Alder condensation with a-cubebane, have been studied. 164 Two new oplopane sesquiterpenes, 196 and 197, have been isolated from Ligularia duciformes, 165 whilst the copacamphane sesquiterpene 198 (dendronobilin A), the picrotoxane derivatives 199-203 (dendronobilins B-F), the cadinane 204 (dendronobilin G) and the cyclocopacamphane 205 (dendronobilin I) have been found in an ethanolic extract from Dendrobium nobile. 166 The known lactones tutin, coriatin and corianin have been obtained from Coriaria sinica.…”

Reactions of Vinylcyclopropane and Bicyclopropyl Compounds With Maleic Anhydride

“…Although Diels-Alder reactions are feasible under a wide variety of conditions, we chose to perform thermal and MWassisted experiments because of their simplicity, and because of the proven "green" character of the latter. It is also of some interest to study the potential subtle differences between these two modes of activation of reagents entering cycloaddition, as has already been observed in our previous works (14).…”

“…Alternative name: 4α,7α-dimethyl-3a,4,7,7a-tetrahydro isobenzofurane-1,3-dione (14) Product 14 was synthesized with a 90-95% yield. 1 Alternative name: 5,6-dimethyl-3a,4,7,7a-tertahydro isobenzofurane-1,3-dione 171 H NMR (CDCl 3 ): 3.36 (tt, 3.5, 1.0; H3a, H7a), 2.46 (td, -15, 1.0, H-4 and H-7), 2.29 (broad d, H-4' and H-7'), 1.717 (CH 3 -C5 and CH 3 -C6) 13 C NMR: 40.3 (C3a and C7a), 30.4 (C4 and C7), 132.7 (C-5 and C-6), 174.46 (C1 and C3), CH3 17.6.…”

“…Cubebene contains the vinylcyclopropane system and undergoes both diene formation and epimerisation under Micro Wave-assisted conditions. Finally; in this work we try to rationalise some of those results by studying simpler diene-generating systems [14,21].…”

“…As an extension of the vinylcyclopropane (1) systems based on bicyclopropyl (2), allyl cyclopropane (3) or cyclopropyl propenes (4) -all of six carbons -could also be considered as potential diene sources. Of course, in order to react as a 1,3-conjugated diene, the cyclopropane moiety (or moieties) of the vinylcyclopropane or bicyclopropyl derivatives should undergo an opening and numerous rearrangements [9][10][11][12][13][14][15].…”