2-Substituted 3-ethynylquinoxalines can be rapidly synthesized in generally excellent yields by a consecutive four-component synthesis starting from electron-rich π-nucleophiles, oxalyl chloride, terminal alkynes, and 1,2-diaminoarenes. The title compounds are highly fluorescent with a pronounced emission solvatochromism. The photophysical properties and electronic structure were additionally corroborated by computations on the DFT level of theory.
Herein the preparative (1 g scale), stereoselective syntheses of various alkyl-substituted g-butyrolactone fragrances 1 is described. The a,b-unsaturated g-keto esters 2 as starting materials were synthesized by a Horner-Wadsworth-Emmons reaction and are further reduced by an ene reductase and alcohol dehydrogenase in a one-pot enzyme cascade to nine desired g-butyrolactones 1, among them whisky (1 c) and cognac lactone (1 d). The products 1 were obtained in moderate to good yields and very good diastereoselectivities. Furthermore, the position of a n Bu-substituent was permutated to study the effect on the enzyme cascade.
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