NOVEL CONCEPTS IN DIRECTED BIARYL SYNTHESIS, 68 : ENANTIOSELECTIVE ORGANICSYNTHESES USING CHIRAL TRANSITION METAL COMPLEXES, 9 : ATROPO-DIASTEREOSELE CTIVE RING OPENING OF BIARYL THIONOLACTONES USING CPRU(S, S)-CHIRAPHOS+ AS A CHIRAL AUXILIARY

The substitution-labile thiophene complex [CpRu{(S,S)-CHIRAPHOS}(SC4H4)]BF4 (2) [(S,S)-CHIRAPHOS = (2S,3S)-bis(diphenylphosphanyl)butane], prepared from [CpRu{(S,S)-CHIRAPHOS}Cl] (1), thiophene, and AgBF4, reacted with the biaryl-thionolactones 3a-f to give the corresponding S-coordinated complexes 4a-f in high yields. The structure of 4c, which crystallized as the pure (S,S,P) diastereoisomer, was determined by X-ray crystallography. Coordination of the ruthenium fragment caused an elongation of the C=S bond, a contraction of the C-O bond within the lactone ring and a flattening of that ring. Single hydride transfer with LiBEt3H converted 4a-f into the thiolactolate complexes 5a-f in good yields and diastereoselectivities. An X-ray structure determination of the major isomer of 5a revealed it to be the (S,S,S,P) diastereoisomer. Protonation with NH4PF6 converted 5a-f into the corresponding ring-opened thioaldehyde complexes 6a-f. Alkylation of 5a with methyl iodide resulted in Ru-S cleavage to give the oxothioacetal 7a and [CpRu{(S,S)-CHIRAPHOS}I](8). Full reduction of 4a-f with LiAlH4 produced the thiolate complexes 9a-f in high yields and 6-74% de. Methylation at sulfur converted 9a-c into the corresponding thioether complexes 10a-c, which were cleaved to 8 and the free methyl thioether 11a-c without isomerization of the biaryl axis.