1.3- Benzodithiol-2-ones, formation

A simple synthesis of symetrically functionalized dithiosalicylides 77a-d from the 377-1,2-benzodithiol-3-ones 75 and triphenylphosphine was described (Scheme 6) <1997JOC9361>. As indicated, the preparation of precursors 75 was based on a known transformation of the substituted anthranilic acid derivatives 73 to the thiosalicylic acid derivatives <1943OSC580>. Upon treatment with thioacetic acid in sulfuric acid, cyclization <1990JOC4693> afforded products 75 in 38-64% yield. Dimerization of a benzothietan-2-one 78a or ketene 78b <1987JOC3838>, arising presumably from initially formed intermediate 76, was proposed to account for the product formation. As revealed... 

Sulfurization of tricoordinated phosphorus compounds by treatment with 3H-1,2-benzodithiol-3-one 1,1-dioxide results from the nucleophilic attack of, for example, a phosphite triester on the electrophilic thiosulfonate function of 2 to produce the phos-phonium sulfinate intermediate 3 (eq 2). Intramolecular condensation of the sulfinate anion with the carbonyl group of the activated thiol ester function releases the phosphorothioate triester (4) with concomitant formation of 5. Because of the... 

However, conversion of the dinucleoside //-phosphonate diester 10 to the phosphorothioate analogue 11 effected by a 0.02 M solution of 2 in 2% aqueous pyridine is relatively slow it reportedly takes 3 h for a complete reaction. While a solution of 2 in 2% aqueous acetonitrile containing triethylamine can completely transform 10 into 11 within 30 s, the use of this sulfurization mixture is incompatible with automated solid-phase oligonucleotide synthesis given the rapid formation of a yellow precipitate caused by triethylamine. In the absence of triethylamine, 10 is not sulfurized under these conditions. Nonetheless, 10 is completely converted to 11 within 20 min when a 0.02 M solution of 1 in 2% aqueous pyridine is used for the sulfurization reaction. Thus, 3i/-l,2-benzodithiol-3-one in aqueous pyridine is compatible with automated solid-phase synthesis of both DNA and RNA oligonucleoside phosphorodithioates or phosphorothioates from appropriate //-phosphonate derivatives. ... 

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