Synthesis of 2,3-dihydrobenzo[f][1,2,5]thiadiazepin-4(5H)-one 1,1-dioxides from polymer-supported α-amino acids is described herein. Different α-amino acids immobilized on Wang resin were sulfonylated with various 2-nitrobenzenesulfonyl chlorides. The resulting 2-nitrobenzenesulfonamides were alkylated with alcohols according to the Fukuyama-Mitsunobu procedure. After reduction of the nitro group and cleavage from the polymer support, the final intermediates were reacted with thionyl chloride, and target compounds of good crude purity and acceptable overall yields were obtained. The chiral HPLC studies revealed the impact of the cyclization step on the resulting stereochemistry. The developed strategy allows for simple production of desired compounds with the application of parallel/combinatorial solid-phase synthesis using commercially available building blocks.
In this work, we attempted to synthesize thioflavonols using rearrangement of phenacyl thiosalicylates prepared by two different approaches and subjected to cyclization under acidic conditions. Contrary to our expectations, the isolated products were identified as (3-hydroxybenzo[b]thiophen-2-yl)(phenyl)methanones. The detailed reaction mechanism was elucidated by characterization of all reaction intermediates with HPLC and NMR spectroscopy. The applicability of the reaction using different phenacyl esters was tested.
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