The intramolecular Buchner reaction of aryl diazoketones. Synthesis and X-ray crystal structures of some polyfunctional hydroazulene lactones
The feasibility of constructing polyfunctional hydroazulenes bearing fused lactone rings via rhodium(II)-catalysed cyclisation of suitably constituted diazoketones followed by catalytic hydrogenation has been examined with respect to both direction and efficiency of cyclisation. The presence of the lactone on the aromatic precursor influences the direction of cyclisation as do substituents at the α-position on the lactone ring. Sulphur-containing substituents inhibit cyclisation. Several new unnatural hydroazulene lactones have been produced. The stereochemistry of hydrogenation of the cyclisation products in two cases has been determined by X-ray diffraction and NMR analysis. Crystals of lactone (34) are monoclinic, space group P21/a, in a cell of dimensions a= 8.625(2), b= 12.993(4), c= 12.109(2)Å, β= 105.79(1)°. Crystals of lactone (42) are monoclinic, space group P21/c, in a cell of dimensions a= 12.885(2), b= 6.115(4), c= 19.417(4)Å, β= 107.14(1)°. The structures were solved by direct methods and refined by full-matrix least-squares calculations; for (34), R= 0.047 for 1405 reflections with l > 3σ(I); for (42), R= 0.045 for 1 370 reflections with I > 3σ(I). The crystal structures establish the relative stereochemistry of hydrogenation of the unsaturated lactones and confirm the direction of cyclisation of the ketocarbenoid intermediates.