Regioselectivity of the Reactions of Heteroatom-Stabilized Allyl ...

Scheme 146
765
762
768 769
(Scheme 146). The chlorine atom seems to play an
important role in the structure of the anions by
intramolecular complexation (CIPE effect). 385-387
b. 1-(Phenylsulfonyl)-2-methylene-3-bromopropane
(See Also Scheme 34). The monoanion of
1-(phenylsulfonyl)-2-methylene-3-bromopropane 770
yields R-products 771 and 773 upon reaction with a
nitroolefin, the syn-isomer 771 being preferentially
formed. The addition of a second molar equivalent
of base to achieve a second deprotonation leads to
increased polymerization. In contrast, reactions with
unsaturated esters give the anti-adducts 772 (cyclization
to 774) as the major products. 388,389 In the
presence of HMPA the diastereomeric ratio for the
esters as acceptors changed to give mainly synproduct
while there was no change with nitropropene.
The influence of chelation evidently favors the
formation of anti-diastereomer, since the chelation
ability decreases for nitropropene. Whereas in case
of R,�-unsaturated esters open chain products 772
could not be detected, only the anti-nitro derivative
773 cyclizes easily forming 775 (Scheme 147). 388,389
3. Sulfur and Nitrogen
763
767
766
764
Monolithiated benzyl[2-(tosylmethyl)-2-propenyl]amine
777 reacts at the R-position to sulfur with D2O,
alkyl halides, propanal, etc. to give 779. Dilithiation
of 776 forming 778 takes place at the R-position and
at the nitrogen to give 780 beside minor 779. Upon
treatment with dihalides as electrophiles, nitrogencontaining
heterocycles 781 result via the adducts
779 and 780 (Scheme 148). 390
4. 2-(Alkylthio)allyl Sulfones and 2-Alkoxyallyl Sulfones
2-Alkylthioallyl sulfones 782 are R-alkylated with
primary alkyl halides, forming 783. A second alkylation
affords R,R-dialkyl sulfones 784. A 1,3-sigmatropic
phenylsulfonyl shift converts 784 into 787
Scheme 147
Scheme 148
705
which is again alkylated at the carbon next to the
sulfonyl group producing 788. 1,2-Dibromoethane
and 1,4-dibromobutane cause dialkylation to give 785
while with 1,3-dibromopropane only the monoalkylated
product is observed (Scheme 149). 391 R,�-
Unsaturated carbonyl compounds react with 782 at
the R-carbon, forming 786 (Scheme 149). 392
By contrast, treatment of disulfone 790 with n BuLi
effects elimination of the sulfonyl group to give the
allene 789. In the presence of an electrophile, e.g.,
methyl iodide, the diene 791 is obtained (Scheme
149). 391