NEW CONVENIENT ONE-POT METHODS OF CONVERSION OF ALKYNES TO CYCLOBUTENEDIONES OR ALPHA,BETA-UNSATURATED CARBOXYLIC-ACIDS USING NOVEL REACTIVE IRON CARBONYL REAGENTS

Reactions of NaHFe(CO)(4)/RX or [HFe3(CO)(11)](-) reagents with alkyne s lead to the formation of the corresponding cr,P-unsaturated carboxyl ic acids and/or the cyclobutenediones. The reagent; generated in situ using the NaHFe(CO)(4)/CH3I combination in THF, on reaction with alkyn es followed by CuCl2. 2H(2)O oxidation, gives the corresponding cyclob utenediones (27-42%) and alpha,beta-unsaturated carboxylic acids (10-2 2%), whereas the reagent generated using CH2Cl2 in place of CH3I leads to a,P-unsaturated carboxylic acids (37-60%) and their derivatives (3 5-55%) at 25 degrees C. The same reagent system in the presence of ace tic acid (4 equiv) yields the corresponding cyclobutenedione (33%). Th e reaction using Me3SiCl gives the corresponding alpha,beta-unsaturate d carboxylic acids (45-54%) at 25 degrees C and the corresponding cycl obutenediones (51-63%) at 60 degrees C. Interestingly, the reaction of the [HFe3(CO)(11)](-) species generated using Fe(CO)(5)/NaBH4/CH3COOH , with alkynes at 25 degrees C, followed by CuCl2. 2H(2)O oxidation gi ves the corresponding cyclobutenediones (60-73%). The possible interme diates and pathways for the formation of alpha,beta-unsaturated carbox ylic acids and cyclobutenediones are discussed.