Novel concepts in directed biaryl synthesis, 68 - Enantioselective organicsyntheses using chiral transition metal complexes, 9 - Atropo-diastereoselective ring opening of biaryl thionolactones using [CpRu{(S,S)-CHIRAPHOS}](+) as a chiral auxiliary
Wa. Schenk et al., Novel concepts in directed biaryl synthesis, 68 - Enantioselective organicsyntheses using chiral transition metal complexes, 9 - Atropo-diastereoselective ring opening of biaryl thionolactones using [CpRu{(S,S)-CHIRAPHOS}](+) as a chiral auxiliary, EUR J INORG, (10), 1999, pp. 1745-1756
The substitution-labile thiophene complex [CpRu{(S,S)-CHIRAPHOS}(SC4H4)]BF4
(2) [(S,S)-CHIRAPHOS = (2S,3S)-bis(diphenylphosphanyl)butane], prepared fr
om [CpRu{(S,S)-CHIRAPHOS}Cl] (1), thiophene, and AgBF4, reacted with the bi
aryl-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. Coordinatio
n of the ruthenium fragment caused an elongation of the C=S bond, a contrac
tion 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 structu
re 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 correspond
ing ring-opened thioaldehyde complexes 6a-f. Alkylation of 5a with methyl i
odide 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 converte
d 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 biar
yl axis.