AN APPROACH TO THE SYNTHESIS OF GELSEMINE: THE INTRAMOLECULAR RAECTION OF AN ALLYLSILANE WITH AN ACYLIMINIUM ION FOR THE SYNTHESIS OF ONE OF THE QUATERNARY CENTRES

Article abstract of DOI:10.1016/S0040-4020(01)86646-1

We describe an efficient synthesis (summarised in Schemes 8 and 10) of an advanced intermediate (34) suitable for the synthesis of gelsemine.The key steps in the synthesis are (i) the Diels-Alder reaction between 1-tetrahydropyranyloxycyclohexa-1,3-diene (10) and methyl β-nitroacrylate (11) giving an adduct (12), in which the chiral centre in the tetrahydropyranyl ring is produced substantially in only one sense, (ii) the rearrangement of a bicyclo<2.2.2>octane (23) into a bicyclo<3.2.1>octane (24), where control of which bridge migrates is achieved by a choice of the counterion in the Lewis acid, and (iii) the efficient formation of the quaternary centre by an intramolecular reaction between an allylsilane group and an acyliminium ion (33 -> 34).