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

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Scheme 39
Scheme 40
222 through 2-(trimethylsilyl)-2,5-dihydrothiophene
1,1-dioxide 220 which is obtained by lithiation and
reaction with Me3SiCl‚NaI. 135
5. Allyl Dithiocarbamates (CdC−C−S−CSNR2)
Pentadienyl dithiocarbamate 223 is alkylated in
the R-position (Scheme 39). 136 Product 224 undergoes
presumably a double [3,3]-sigmatropic rearrangement
to form 226. 137 Treatment of the latter with MeI
gives 1-iodo-2,4-(E,E)-dienes 225 (or tetraenes depending
on R). 138 Pheromone synthesis has proceeded
via these steps. 139,140
R-Products 228 and 229 are usually obtained in the
reaction of allyl dithiocarbamate anions from 227
with aldehydes via titanium reagents (Scheme 40). 141
In the absence of Ti(O i Pr)4, both the R- and γ-products
are observed. 142-144
6. Allylsulfinamides (CdC−C−SONR2)
Prepared from allyl alcohols and 4-(chlorosulfenyl)morpholine
in the presence of triethylamine, allylsulfinamides
230 undergo R-alkylation apparently
with high regioselectivity to 231 (Scheme 41), 145
although Julia reported a low diastereoselectivity
except for R 1 ) p-Me-C6H4, R 2 ) H. 146 No isomerization
of the double bond in 231 was detected after the
alkylation. Reaction of 230 with aldehydes gives the
R-anti-adducts (�-hydroxysulfinamides) 232 which
are unstable and can be converted into the corresponding
polyene 233 (mainly E product) by heating
under reflux in toluene (Scheme 41). 145 The yield of
the alkyl sulfide anion is improved by using methyllithium
as the metalating agent since butyllithium
can lead to side reactions.
Scheme 41
7. Allyl Sulfoximines (CdC−C−SONR)
The thermal rearrangement of allylic sulfoximines
234 to allylic sulfinamides 236 can occur thermally
but only in a few cases. 147a,b However under palladium(0)
catalysis this rearrangement is a general
and facile process. 147c,d The rearranged products 236
can be converted to N-protected allylic amines by
mild base hydrolysis. The alkylation of allylic sulfoximines
234 (R 1 ) Ph, CH2Ph, R 2 ) Tol) gives
R-alkylated products 235 as mixtures of diastereoisomers.
148 An optically active allylic sulfoximine gave
an R-alkylated product as a single diastereoisomer. 147c
Reaction of lithiated 234 (R 1 ) Ph; R 2 ) Tol) with
benzaldehyde gave a 5.3:1 mixture of the R-adduct
238 and the γ-product 239, while a similar reaction
with pivaldehyde yielded only the R-product 238. 148
In related examples, R-products were exclusively
formed from the reaction of lithiated N-tert-butyldiphenylsilyl
149a and N-methyl 149b allylic sulfoximines
with aldehydes. Lithiation of racemic N-tosyl allylic
sulfoximine 234 (R 1 ) Ts; R 2 ) Ph) followed by
quenching with benzaldehyde or isobutyraldehyde
gave exclusively the R-product 238 as mixtures of
diastereoisomers. 149c
The reaction of lithiated sulfoximines 234 with
cyclic enones gave mixtures of regio- and diastereoisomers.
The regioselectivity is dependent on the
nature of the N-substituent. 148,149a,150,151 N-Tosyl derivatives
give exclusively R-1,4-products 240, while
this orientation of adduct is only slightly favored in
the case of the N-phenyl derivatives. N-tert-Butyldiphenylsilyl
derivatives, by contrast, favor γ-1,4adducts
(241).
For acyclic enone cases, the regioselectivity is also
influenced by the nature of the R 1 and R 2 on 234 and
the reaction conditions, while the diastereoselectivity
can be achieved. 149a,150,151a In one case, the addition
of acyclic enones to the lithiated N-tosyl-S-allyl-Sphenylsulfoximines
in THF at ∼78 °C followed by
quenching with acetic acid at same temperature
produced exclusively the 1,4-R-adducts 243 with high
diastereoselectivity (Scheme 43). 150 Warming a solution
of the anionic adducts 242 to room temperature
gave the racemic vinylcyclopropanes 244.
Diastereomerically pure γ-hydroxyvinyl sulfoximide
is obtained with titanium reagents (Scheme
44). 152,153