y momose t tetrahedron 1991 47 7635 it was observed however that following the reaction conditions described in the literature failed to afford the desired product iii in significant yield it was discovered that the addition of a phosphine oxide compound of the formula r 1 3 po wherein r 1 is c 1 6 alkyl or aryl was necessary for the reaction to proceed efficiently step c is performed in an aprotic organic solvent suitable aprotic organic solvents for this step include for example tetrahydrofuran toluene dichloromethane dichloroethane or chloroform suitable lewis acids for use in this step include for example alcl 3 ticl 4 and trialkylaluminums of the formula c 1 6 alkyl 3 al such as me 3 al suitable phosphine oxides for this step include for example triarylphosphine oxides such as triphenylphosphine oxide wherein the phenyl groups are optionally substituted with one or more methoxy or amino groups when the acid compound of formula iib is employed in step c a coupling agent is used to cause cyclization via an intramolecular coupling between the carboxylic acid group and the amine group i e a peptide type coupling reaction suitable coupling agents for this purpose include conventional peptide coupling agents for example acetic anhydride acetyl chloride thionyl chloride and oxalyl chloride suitable aprotic organic solvents for this step are the.