"Transmission of Chiral Information through conjugation."

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The streochemical sense of both gamma-sulfenyl and-alkoxy substrates is consistently interpreted by situating the most electron-donating group orthogonal to the enone face concurrent with the back-side attack of the nucleophiles. Although the back-side attack may possibly be induced simply by the steric bulk of the substituent in the orthogonal position, we rather advance that the stereoelectronic origin is more plausible on the basis of only a small difference between the phenythio and methylthio derivatives as well as the results with alpha-enals. More significantly, the stereochemical outcome with gamma-siloxy alpha-enones is not consistent with the steric argument because the back-side attack should be hampered by the largest siloxy group resulting in the opposite sense of the stereoselectivity if the steric origin is valid. Obviously, the precise picture of the mechanism would be drawn by dealing with transition states, not with the ground states.