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

680
Scheme 46
Scheme 47
1. Allylamines (CdC−C−NR2)
Lithiated allylamines 260 are prepared by deprotonation
of enamines 258 or allylamines 259. 157
γ-Products 261, 263, and 264 result exclusively or
predominantly for reactions with TMSCl, 157 bulky
alkyl halides, carbonyl compounds, and epoxides
(Scheme 46). 158 The hydroxy derivatives produced
from the carbonyl compounds and epoxides give upon
heating dihydrofurans 262 and dihydropyrans 265,
respectively. 159 The resulting silylated enamines can
be lithiated again and react with RX to give R-products
with respect to the trimethylsilyl group. 157
However, in some cases additional substituted products
are found as in the reactions of [CdC-C-N(Me)-
Ph] with Me3SiCl, RX, RCHO, and RCOR. 160-162 For
example a mixture of the R- and γ-products was
obtained with methyl iodide. 163
Lithiated allyldiphenylamine 266 gives the γ-adducts
268 [(E)-allylboranes] with (-)- and (+)-B-
(methoxydiisopino)campheylborane 267 and boron
trifluoride-diethyl etherate. Upon treatment with
aldehydes, 268 provides anti �-diphenylamino alcohols
269 which are γ-adducts with respect to boron
and R-adducts to the nitrogen. The reaction proceeds
with excellent anti-relative stereochemical control
(Scheme 47). 164
2. 1-Allylpyrrolidines (CdC−C−N(CH2)4), 9-Allylcarbazoles
(CdC−C−Cb), and N-Allylbenzotriazoles (CdC−C−Bt)
The anions from 1-allylpyrrolidine 270 and 9-allylcarbazole
274 165 are both alkylated at the γ-terminus
in high yields to give (E)-273 and (Z)-276,
Scheme 48
Scheme 49
respectively. In contrast, reactions of 1-allylpyrrolidine
anion with carbonyl compounds exhibit low
regioselectivity to form equal amounts of R- 272 and
γ-products 271. 166 Application of Zn 2+ as the counterion
favors the formation of the R-adduct 272. 167
9-Allylcarbazole reacts with ketones mostly at the
R-position to form 275, 168 while 1-allylbenzotriazole
277 generally gives the R-products 278 with alkylating
agents and carbonyl derivatives (Scheme 48). 169
Enantiomerically pure 1-allyl-2-(S)-methoxymethylpyrrolidine
279 is γ-alkylated with high diastereoselectivity
to yield enamine 280 (Scheme 49). 170 The
diastereoselectivity varies with the nature of the
counterion, the solvent and the reaction temperature.
The better solvated lithium salt (cf. 281) gives a lower
d.e. in THF than the potassium salt while changing
to less complexing petrol ether causes a significant
increase of the diasereoselectivity.