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Mechani
stic
studie
s on the intramolecular nucleophilic
sub
stitution with allylic rearrangement (S
Ni' reaction)and a new
stereo
selective acce
ss to
sub
stituted cyclobutanone
s are reported. 4,4-Dialkyl-5-oxohex-2
E-en-1-yl methane
sulfonate
s 4 were converted to 2,2-dialkyl-3-vinylcyclobutanone
s 6 by S
Ni' ring clo
sure.The
stereochemical analy
si
s of the reaction wa
s achieved through ring clo
sure of (6
S)-6-chloro-3,3-diethylhept-4
E-en-2-one (
S)-
17, defined by the ab
solute configuration of C(6), leading to (3
S)-2,2-diethyl-3-(prop-1
E-en-1-yl)cyclobutanone (
S)-(
E)-
18 and (3
R)-2,2-diethyl-3-(prop-1
Z-en-1-yl)cyclobutanone (
R)-(
Z)-
18, in a ratio of 85:15, with almo
st complete tran
sfer of chirality (>97%). The ab
solute configurationof (
S)-
17 wa
s determined by X-ray diffraction analy
si
s of the camphanoate derivative
16. The ab
soluteconfiguration of the cyclobutanone product
s (
S)-(
E)-
18 and (
R)-(
Z)-
18 wa
s determined by Raman opticalactivity
spectro
scopy. Compari
son of the ab
solute configuration of (
S)-
17 and the re
sulting (
E)- and(
Z)-cyclobutanone
s 18 allowed the conclu
sion that the S
Ni' reaction proceed
s with
syn geometry relativeto the leaving group.