DIOXOPYRROLINES .30. A NOVEL ERYTHRINAN AND HOMOERYTHRINAN SYNTHESIS BY TETRA-N-BUTYLAMMONIUM FLUORIDE INDUCED OXY-VINYL 1,3-SHIFT - SYNTHESIS OF A 6-METHOXYCARBONYL-2,8-DIOXO-1,7-CYCLO-B-HOMO-ERYTHRINAN, A POTENTIAL INTERMEDIATE TO SCHELHAMMERA ALKALOIDS