Tied-back esters

Many commercial sulfonylureas contain an ortho ester, therefore, preparation of tied-back ester was of great interest. We could use the target intermediate monomethylamide 2 (Scheme X), as both a directing group for metallation and as the latent lactone group. The sulfonamide handle could be added via metallation and quenched with propyl disulfide. Sulfide 2Q can also be prepared via a nucleophilic displacement of the chlorobenzamide 21. A second metallation of 2Q gave the ethanol derivative 22. Base hydrolysis to the amide to the carboxylate, then lactonization under acidic conditions, gave the isocoumarin 22. Oxidative chlorination and amination proceeded without a problem. 

Herbicidal Activity of Tied-Back Esters vs Open-Chain Esters... 

Another advantage is that the final purification and working up of the wa waters can be tied in with the production of the crude ester. Figure 12-6 illustrates the essentials of this process. The raw materials are first blended in the correct proportions and fed from the feed tank in a steady stream throu a preheater into the esterifying column. From the top of the column is taken off a mixture of about -20 per cent ester, 10 per cent water, and 70 per cent alcohol, while a suitable amount of the same distillate is refluxed back to the column at (A). The ternary mixture taken off passes... 

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