“…In order to demonstrate that such intermediates could be used to perform the desired ring closing aldol reaction, one of them (6a) was hydrolysed to acid 7 and converted to malonamide 8 by DCC coupling with oxazolidine 1. Furthermore, during the course of this work, we found that acyl Meldrum's acids 5b-d could be opened directly with oxazolidine 1 (R ¼ H), 15,16,19,20 giving malonamides 9a-c very efficiently; these sequences provided access to variously substituted analogues replacing the methoxy group at the chain terminus of 8. We also expected that intermediates of type 6 would prove to be pivotal, since alkylation at either or both of the aand g-positions using standard conditions should be possible, providing access to diversely functionalised pyroglutamates aer cyclisation.…”