J. Varga, J. Rábai, F. Ruff
Nov 28, 2003
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Journal
Tetrahedron-asymmetry
Abstract
Abstract ( S )-(+)- and ( R )-(−)-enantiomers of naphthyl-phenyl-bis(acyloxy)spiro-λ 4 -sulfane 2 were prepared from the precursors ( R )-(−)- and ( S )-(+)-naphthyl phenyl sulfoxide dicarboxylic acid 2a with acetic anhydride. The hydrolysis of spiro-λ 4 -sulfane ( R )-(−)- 2 in acidic and basic solutions gave as major products sulfoxide ( S )-(+)- 2a and ( R )-(−)- 2a , respectively. The selectivity of the reactions was interpreted with the different reactivities of the ortho and peri neighboring carboxylic groups of the sulfoxide 2a , and with the different ability of the five and six-membered rings to be cleaved in spiro-λ 4 -sulfane 2 . The absolute configurations of the enantiomeric spiro-λ 4 -sulfanes 2 and sulfoxides 2a were determined by CD spectroscopy. Exciton coupling was observed in the spectrum of spiro-λ 4 -sulfane 2 between the benzene 1 L a and naphthalene 1 B b transitions, which results in a negative couplet for ( R )-(−)- 2 . Exciton coupling can be expected only for the 1 B b transitions of the S -phenyl and S -naphthyl rings of the sulfoxides, which define a positive couplet for ( S )-(+)- 2a . Empirical rules were found to be valid for the determination of configuration of spiro-λ 4 -sulfanes and related sulfonium compound derivatives with a trigonal bipyramidal structure, and for that of naphthyl-phenyl-sulfoxides. Both spiro-λ 4 -sulfanes and sulfoxides should be viewed from the side of the lone pair; the axial substituents in the former case and the downwards oriented SO bond in the latter case are placed in a vertical plane. Rings and substituents in the upper-right and lower-left sectors define positive exciton couplets, while the opposite case is characterized by negative exciton-coupled circular dichroism (EC-CD).