I. Approaches to the synthesis of a symmetrical cyclopropenyl anion. II. Hydrophobic effects on organic displacement reactions in water

I. Due to the interesting properties of cyclopropenyl anions, including antiaromaticity and a possible triplet ground state, they have been the target of numerous synthetic efforts over many years. In this work, we have attempted to synthesize a tricyanocyclopropenyl anion that would be stable in solution and exist as a symmetrical, planar, ground state triplet. Since earlier attempts to deprotonate electron deficient cyclopropenes with base have failed, we have devised several strategies for concealing the reactive double bond of tricyanocyclopropene in attempt to prevent unwanted side reactions. We have attempted to synthesize a bis(trimethylsilyl)tricyanocyclopropane also containing a leaving group X. Such a molecule could be converted to a transient (trimethylsilyl)tricyanocyclopropene by fluoride induced elimination of Me₃Si-X, which could then be fluorodesilylated to the desired tricyanocyclopropenyl anion under the same reaction conditions. We have also made Diels-Alder adducts of tricyanocyclopropene in the hope of deprotonating the cyclopropane of the adduct followed by a retro Diels-Alder to generate a cyclopropenyl anion.; II. The rates of the Diels-Alder reaction and the benzoin condensation are increased in water due to the hydrophobic effect. Cosolvents and other antihydrophobic additives can be used probe for changes hydrophobic effects on reactions. In this work we investigate the role of hydrophobic effects on reaction rates and product selectivity of S _N2 reactions in water. We have examined various displacement reactions of ambident phenoxide nucleophiles in aqueous solution. We have used cosolvents to observe how small changes in the solvent properties effect the rates and product distributions of aqueous phenoxide alkylations. We have combined our interpretations of cosolvent effects with careful control reactions and some computational data to create a revised picture of the alkylation of phenoxides, incorporating effects stemming from both the nucleophile and the electrophile and their mutual interaction in aqueous solution. We find that hydrophobic packing of alkyl substituents on a phenoxide nucleophile against a benzylic electrophile in water drives the reaction in favor of carbon alkylation over the usual alkylation of the oxygen in non-aqueous solvents.