| Abstract
| - Mechanistic studies on the intramolecular nucleophilic substitution with allylic rearrangement (SNi‘ reaction)and a new stereoselective access to substituted cyclobutanones are reported. 4,4-Dialkyl-5-oxohex-2E-en-1-yl methanesulfonates 4 were converted to 2,2-dialkyl-3-vinylcyclobutanones 6 by SNi‘ ring closure.The stereochemical analysis of the reaction was achieved through ring closure of (6S)-6-chloro-3,3-diethylhept-4E-en-2-one (S)-17, defined by the absolute configuration of C(6), leading to (3S)-2,2-diethyl-3-(prop-1E-en-1-yl)cyclobutanone (S)-(E)-18 and (3R)-2,2-diethyl-3-(prop-1Z-en-1-yl)cyclobutanone (R)-(Z)-18, in a ratio of 85:15, with almost complete transfer of chirality (>97%). The absolute configurationof (S)-17 was determined by X-ray diffraction analysis of the camphanoate derivative 16. The absoluteconfiguration of the cyclobutanone products (S)-(E)-18 and (R)-(Z)-18 was determined by Raman opticalactivity spectroscopy. Comparison of the absolute configuration of (S)-17 and the resulting (E)- and(Z)-cyclobutanones 18 allowed the conclusion that the SNi‘ reaction proceeds with syn geometry relativeto the leaving group.
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