Coumarins imino

Somewhat unexpectedly, the 1-dansylamino derivative 193 (Scheme 58) of the 3-glucosidase inhibitor 2,5-dideoxy-2,5-imino-D-mannitol turned out a nanomolar inhibitor (K 2.4 nM) of Agrobacterium sp. (3-glucosidase.382 The same was true when the fluorophor and the inhibitor were separated by a C6 spacer arm. Equally active were the corresponding coumarin-3-carboxylic acid derivative 66 (Scheme 18 ... 

The moisture- and air-stable ionic liquids, l-butyl-3-methylimidazolium tetra-lluoroborate [bmim]BF and l-butyl-3-methylimidazolium hexafluorophosphate [bmim]PFg, were used as green recyclable alternatives to volatile organic solvents for the ethylenediaimnonium diacetate-catalyzed Knoevenagel condensation between aldehydes or ketones with active methylene compounds. As described by Su et al. [57], the ionic hquids containing a catalyst were recycled several times without decrease in yields and reaction rates. In the case of 2-hydroxybenzaldehyde, the reactions led to the formation of 3-substituted coumarin derivatives in high yields of up to 95% (Scheme 17.11). When ethyl cyanoacetate was used, 2-imino-27f-l-benzopyran-3-carboxyhc acid ethyl ester was formed. 

More recently, the same group reported that acetic anhydride can also act as an electrophile to trap the zwitterionic intermediate 109 and developed a three-component synthesis of 2,5-dihydro-5-imino-2-methylfuran-3,4-dicarboxylates [74]. More significantly, they developed an elegant four-component synthesis of 3,4-dihydro-coumarin derivatives by reaction of salicylaldehyde, Meldrum s acid, isocyanide, and... 

Condensation of 4,6-dimethoxy-2-hydroxyacetophenone with diethyl carbonate and an alkoxide ion has now been shown to give the coumarin-3-carboxylic ester (245), and not 4-hydroxy-5,7-dimethoxycoumarin (246), as originally reported. Heating the ester with aqueous alkali resulted in hydrolysis and decarboxylation to (246). The well-established acid cyclization of salicyl-aldehyde with ethyl cyanoacetate to give coumarin-3-carboxylic acids has been studied in alkaline media and found to give the ester (247 X = O) and the imino-ester (247 X = NH). When the proportion of the cyano-ester was increased, high yields of the latter were obtained. "... 

Incorporating these acceptors into various chromophore architectures. Harper has shown that for the pyrazolone anil blue shifting has indeed been achieved while maintaining a relatively high optical nonlinearity. Unfortunately, utilization of pyrazolone anil chromophores has been hampered by unacceptably low yields. A more acceptable alternative appears to be the imino-coumarin shown below ... 

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