MANGANESE-MEDIATED CARBON-CARBON BOND FORMATION IN AQUEOUS-MEDIA - CHEMOSELECTIVE ALLYLATION AND PINACOL COUPLING OF ARYL ALDEHYDES

The use of manganese as a mediator for allylations and pinacol couplin gs in aqueous media was investigated. The combination of manganese and copper is found to be a highly effective mediator for the allylation of aryl aldehydes in water. Such a combination is found to be more rea ctive than other previously reported metals in aqueous media. No react ion was observed with either manganese or copper alone as the mediator . Only a catalytic amount of copper is required for the proceeding of the reaction. The uses of Cu(0), Cu(I), and Cu(II) as the copper sourc e are all effective. The use of a catalytic amount of manganese combin ed with a stoichoimetric amount of copper led to the failure of the re action. Allyl chloride is found to be more effective than allyl bromid e for the corresponding reaction. The use of substituted allyl halides gave-a mixture of regio- and diastereoisomers. Aromatic aldehydes rea cted chemoselectively in the presence of aliphatic aldehydes. An exclu sive selectivity was also observed when both an aliphatic and an aroma tic aldehyde functionalities are present in the same molecule. In the presence of acetic acid or ammonium chloride, manganese was found to e ffect the pinacol-coupling reaction in water. The reaction proceeds se lectively with aryl aldehydes.