New series of ethyl 5-substituted 2,3-dihydro-3-oxoisothiazolo[5,4-b]pyridine-2-acetate was prepared either a) directly by reaction of 5-substituted 2chlorothio-3-pyridinecarbonyl chlorides with ethyl glycinate orb) by oxidation of the correspondent 2-mercapto-3-pyridinecarboxamides. New 5-substituted 1 3 dihydro-2-thioxo-3-pyridinecarboxylic acids as starring materials are described.

Several ethyl 2,3‐dihydro‐3‐oxoisothiazolo[5,4‐b]pyridine‐2‐alkanoate derivatives were synthesized as herbicides. Only 5‐methyl derivatives inhibited both hypocotyl and root growth in the lettuce (Lactuca sativa L.) seedling test at 100 mg litre‐1. Only ethyl propionate and valerate derivatives showed significant inhibition at 0·1 mg litre‐1, whereas ethyl acetate or butyrate derivatives were inactive. Contrary to unoxidized derivatives, the inhibitory effect of 1‐oxide and 1,1‐dioxide derivatives was strongly dependent on concentration; ethyl 2,3‐dihydro‐5‐methyl‐3‐oxoisothiazolo[5,4‐b]pyridine‐2‐propionate 1,1‐dioxide inhibited 100% of germination at 100 mg litre‐1 and 45% of lettuce seedling growth at 0·1 mg litre‐1. Quantitative structure–inhibition of growth relationship analysis carried out by adaptive least‐squares (ALS) method gave a good correlation with small and hydrophobic 5‐substituents as well as with odd carbon‐chain ethyl alkanoates in position 2. Active compounds did not show auxin‐like activity from 0·1 to 100 mg litre‐1. © 1997 SCI.

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: Several ethyl 2,3-dihydro-3-oxoisothiazolo [5,4-b]pyridine-2-alkanoate derivatives were synthesized as herbicides. Only 5-methyl derivatives inhibited both hypocotyl and root growth in the lettuce (L actuca sativa L.) seedling test at 100 mg litre~1. Only ethyl propionate and valerate derivatives showed signiÐ-cant inhibition at 0É1 mg litre~1, whereas ethyl acetate or butyrate derivatives were inactive. Contrary to unoxidized derivatives, the inhibitory e †ect of 1-oxide and 1,1-dioxide derivatives was strongly dependent on concentration ; ethyl 2,3-dihydro-5-methyl-3-oxoisothiazolo[5,4-b]pyridine-2-propionate 1,1-dioxide inhibited 100% of germination at 100 mg litre~1 and 45% of lettuce seedling growth at 0É1 mg litre~1. Quantitative structureÈinhibition of growth relationship analysis carried out by adaptive least-squares (ALS) method gave a good correlation with small and hydrophobic 5-substituents as well as with odd carbon-chain ethyl alkanoates in position 2. Active compounds did not show auxin-like activity from 0É1 to 100 mg litre~1.