The regio- and diastereoselectivities of metal-mediated allenylation of carbonyl compounds were investigated in aqueous media. Different metal mediators showed varied regioselectivities on product formation during propargylation-allenylation reactions of carbonyl compounds with simple propargyl bromide. Under the standard reaction conditions, the use of indium provided the highest regioselectivity, with a preference of formation of the homopropargyl alcohol. The use of tin and bismuth as the metal mediator provided slightly lower selectivities with the same preference. The use of zinc and cadmium as the mediators further lowered the product selectivity. The reactions of an aliphatic aldehyde with simple propargyl bromide showed a lower selectivity than the reaction of an aromatic aldehyde in most cases, except for the use of tin or zinc (where comparable selectivities were observed). On the other hand, the reaction of terminal-substituted propargyl bromides with aldehydes mediated by indium showed a high regioselectivity in forming allenylation products. The indium-mediated allenylation of carbonyl compounds bearing an alpha-hydroxyl group also proceeded with a high diastereoselectivity, forming syn-diols predominantly in aqueous ethanol. The high diastereoselectivity in allenylation of alpha-hydroxyl-substituted aldehydes was attributed to the chelation effect exhibited by the alpha-hydroxyl substitutent. Through the use of this highly diastereoselective allenylation, (+)-goniofufurone was synthesized from D-glucurono-6,3-lactone.

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Metal-mediated carbonyl additions were investigated using several alternative media. Using the allylation as a model, metals were examined across the periodic table in mediating carbonyl additions in water. The effectiveness of metals as the mediator for the reaction was found closely related to the location of the metals in the periodic table and was tentatively rationalized via inner-sphere and outer-sphere single-electron -transfer processes. It was also found that, for allylation of aldehydes, water, liquid carbon dioxide, and neat conditions are all effective media when metals such as indium, tin and zinc were used as the mediators. Various homoallyl alcohols were prepared by these reactions. Under these conditions, allyl halides were found much more reactive than other types of organic halides. The cause for the special reactivity of allyl halides as well as the mechanism for forming allylmetal intermediates is discussed. 178

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