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

704
Scheme 141
Scheme 142
section V.B.1) which are lithiated exclusively at the
sp 3 carbon and form allylic anions.
Lithiation of (E)-N-(3-tosyl-2-propenyl)morpholine
752 with s-BuLi takes place in the vinylic position
to give the corresponding γ-functionalized organolithium
intermediate 753. The further reaction of this
anion with D2O, alkyl halides, aldehydes, or ketones
affords regio- and stereoselectively tosylated γ-functionalized
allylmorpholines 754 (Scheme 143). 381a
Scheme 143
2. γ-Silyl Enamines (R2N−CdC−C−SiMe3)
γ-Silylated enamines 755 are alkylated at the
carbon adjacent to silicon forming 756 (Scheme
144). 157
Scheme 144
E. Others
This section deals with two classes of compounds
which cannot readily be allocated to one of the
previously mentioned subdivisions: each contains
two heteroatoms, in the first class (sections E.1 to
E.3) while one heteroatom is part of the allylic
system, the other heteroatom is linked to the �-allyl
carbon via a methylene group. Deprotonation could
give alternative allylic anions stabilized by either
heteroatom. The second class (section E.4) combines
1,2-heterosubstituted allyl anions.
1. 2-(Tosylmethyl)-2-propen-1-ol (See Also Scheme 34)
2-(Tosylmethyl)-2-propen-1-ol 757 on treatment
with BuLi forms dilithiated dianion 758 which gives
R-adducts 759 with alkyl halides and aldehydes. The
product 759 obtained with tert-butyl bromoacetate as
electrophile cyclizes to the corresponding δ-lactone
760 by treatment with 30% trifluoroacetic acid (TFA)
(Scheme 145). 381b By contrast, conjugate addition of
758 to nitroolefins occurs at the γ-position to tosyl,
forming 761 (Scheme 145). 382
Scheme 145
2. Sulfur and Halogen
a. 2-(Chloromethyl)-3-tosylpropene. The R-adduct
763 of the monolithiated derivative 762 can be
transformed into a diene 764. 383,384 2-(Chloromethyl)-
3-tosylpropene dianion 765 is alkylated exclusively
at the R-position; reactive alkylating agents yield R,Rproducts
766 while less reactive agents afford products
767 obtained by γ-elimination. The reaction of
765 with aldehydes yields the corresponding tosylated
dihydrofurans 768. 385,386 Ketones reacted with
the dianion at the less-hindered γ-position to give 769