PYRYLIUM-SALTS IN POLYENE NATURAL PRODUCT SYNTHESIS - ORGANOMETALLIC ADDITIONS TO 4-METHYLPYRYLIUM TETRAFLUOROBORATE

The synthetic utility of organometallic additions to pyrylium salts as a procedure for the stereocontrolled preparation of 2Z,4E-dienals, an d the use of these compounds in polyene natural product synthesis, is summarised. The extension of this methodology to 4-methylpyrylium tetr afluoroborate to give a new route to 3-methyl-2Z,4E-dienals via a six- carbon organometallic homologation procedure is then described. Finall y, the utilisation of this methodology to provide a concise synthetic approach to 13Z-retinal, retinal and a range of retinal analogues is t hen elaborated.