Nitroacrylates : versatile reagents in organic synthesis
Nitroacrylates are stable, crystalline solids and have frequently been used in synthesis as reactive dienophiles in the Diels-Alder reaction. The regio- and diastereoselectivity of the Diels-Alder reaction is controlled by the electronic properties of the nitro group. This thesis describes work to utilise the nitro group to provide control of stereochemistry in the synthesis of natural products. The thesis begins by discussing the synthesis of nitroacrylates using both a nitro-aldol and radical based route. An investigation into their selectivity in the Diels-Alder reaction with a diverse array of dienes is discussed. As part of this investigation a large increase in diastereoselectivity was observed for the reaction of ethyl β-nitroacrylate and 1-methoxycyclohexa-1,4-diene when Lewis acids were added. The origin of this selectivity is unknown and similar dienes show only a modest increase in selectivity on addition of ZnCl(_2).An application of the resultant adducts has been demonstrated in the synthesis of a simple bicyclic P-amino acid and then subsequendy applied to the diastereoselective synthesis of chorismate-based P-amino acids (25*, 3S*)-DHAA and the antibiotic oryzoxymycin. The key steps involve a base-mediated ring-opening reaction of the 7-oxa-bicyclo[2,2,l]hept-5-ene and a CsF mediated coupling of the lactate moiety. The progress toward the synthesis of a related anthranilate synthase inhibitor is also discussed. Finally, in the context of a synthesis of the structurally unique diterpene Vinigrol 1 we have shown that nitroacrylates can be employed as substituted ketene equivalents in the formation of cyclic alpha-chiral ketones.