Potassium Triiodide. A New and Efficient Catalyst for Carbon–Carbon Bond Formation in Aqueous Media Ashim J. Thakur, Dipak Prajapati,  Baikuntha J. Gogoi, and Jagir S. Sandhu  Regional Research Laboratory, Jorhat 785006, Assam, India (Received November 22, 2002; CL-020997) Potassium triiodide catalyses the condensation of carbonyl compounds with active methylene compounds in aqueous media to afford E olefinic products in high yields. There has been growing interest in the use of metallic elements 1 in aqueous media, as they offer significant advantages over conventional reactions using dry organic solvents. The development of such reactions is of interest because they also offerthepossibilityofobtainingenvironmentallybenignreaction conditions by reducing the burden of organic solvent disposal. 2 The study and application of Knoevenagel condensation in water is still in its infancy. Since their century old history the full synthetic potential of such reactions is still waiting to be explored and they need to be expanded. 3 In recent years there has been increasing emphasis on the use of environment friendly condi- tions to reduce the amount of toxic waste and by-products arising fromthechemicalprocesses.Thechallengeistodevelopcatalytic conditions leading to carbon–carbon bond formation which are widely employed in organic synthesis. The Knoevenagel con- densation, have numerous applications in the elegant synthesis of fine chemicals, 4 in hetero Diels–Alder reactions, 5 inthesynthesis of carbocycles and heterocycles 6 and are usually catalysed by organic bases (primary, secondary and tertiary amines, ammonia and ammonium salts). With piperidine base, the by-products formed are difficult to remove. 7 However, in recent years, new catalysts 8 including silica gel functionalised with amine groups (Al 2 O 3 , AlPO 4 –Al 2 O 3 , TiCl 4 /base and doped xonontlite), solid phase resin, 9 CdI 2 in solid 9 state, MS 5A/ethylenediammonium diacetate 10 and MW 11 have been employed. But these methods havetheirownmeritsaswellaslimitations.Themainhurdlewith the Knoevenagel condensation is the reactivity of ketones with thecompetitiveMichaeladditionoccuringinthereactionofsome active methylene compounds and there is also problem with the stereocontrol in the synthesis of Knoevenagel products from unsymmetrical carbonyl compounds. Here we wish to report the first example of a new catalyst Kl 3 , for carbon–carbon bond formation in aqueous condition. It can perform the reaction to producethe E olefinicproductsingoodpurityandhighyields,and eliminates the piperidine based by-products and reduces trans- esterification. The results obtained with different aliphatic, aromatic and heterocyclic aldehydes and different active methylene com- pounds, according to scheme 1 are recorded in the table. Also it can be seen from the table that all reactions proceeded selectively tothedehydratedproductswithoutanysidereaction.Thereaction between benzaldehyde and ethyl cyanoacetate in the presence of KI 3 (entry 3g) gave selectively the Knoevenagel adduct while the same reaction promoted by an alkali metal containing MCM-41 yielded a mixture of hydrated and dehydrated products. 12 The aromatic a; b-unsaturated aldehydes gave the corresponding olefinic products without the formation of any Michael-type addition products. Thus, cinnamaldehyde with malononitrile gave 1,1-dicyano-4-phenylbuta-1,3-diene (90% conversion after 20 min) exclusively. In the reaction of o-hydroxybenzaldehyde with active methylene compounds the first-formed Knoevenagel condensation products underwent further transformations as a result of nucleophilic attack by the phenolate ion on the cyano group, which is held in a stereochemically favourable position by the olefinic bond. Thus 2-imino-2H-1-benzopyran-3-carbonitrile and 2-imino-2H-1-benzopyran-3-carboxylate were formed ex- clusively in 82 and 85% yields. The reaction 13 was carried out by mixing carbonyl compound, active methylene compound and potassium triiodide 14 at room temperature and heating them at 70  C for a specified time period, to give after usual work-up excellent yields of the corresponding Knoevenagel products. Some yields (e.g. 3a, 98%) were much higher than reactions carried out in boiling benzene (74%). Furthermore, the rate of the R 1 H O R 2 R 3 + KI 3 R 1 H R 2 R 3 Scheme 1. Table 1. Reaction time and yield of Knoevenagel product 3 Prod- R 1 R 2 R 3 Reaction Yield ucts time/min /% 3a Ph CN CN 15 98 3b (E)-PhCH=CH CN CN 20 88 3c Me CN CN 20 80 3d 2-Furyl CN CN 22 80 3e 4-Quinolyl CN CN 21 85 3f p-NO 2 C 6 H 4 CN CN 16 83 3g Ph CO 2 Et CN 15 86 3h (E)-PhCH=CH CO 2 Et CN 20 85 3i p-NO 2 C 6 H 4 CO 2 Et CN 16 87 3j 2-Furyl CO 2 Et CN 20 82 3k 4-Quinolyl CO 2 Et CN 18 83 3l Ph CO 2 H CN 16 89 3m (E)-PhCH=CH CO 2 H CN 15 85 3n Ph CONH 2 CN 15 90 3o (E)-PhCH=CH CONH 2 CN 20 90 3p p-MeOC 6 H 4 CONH 2 CN 22 90 3q Ph CO 2 Et CO 2 Et 20 85 3r Ph MeCO CO 2 Et 22 80 3s o-OHC 6 H 4 CN CN 20 82 3t o-OHC 6 H 4 CN CO 2 Et 22 80 258 Chemistry Letters Vol.32, No.3 (2003) Copyright Ó 2003 The Chemical Society of Japan