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

702
Scheme 131
(cf. 701, Scheme 131) at the R-position to the sulfonyl
group. 356 SiO2-catalyzed 1,3-rearrangement of 701
gives 1-(methylthio)-1-(p-tolylsulfonyl)-2-propene derivatives
700, which using NaH in DMF are then
alkylated at the R-position to produce 702. Subsequent
hydrolysis of 702 affords the R,�-unsaturated
ketones 703 (Scheme 131). 363
5. 1-(Benzotriazolyl)-3-(dialkylamino)-2-propenes
(Bt−C−CdC−NR2)
1-(3-Morpholinoprop-2-enyl)benzotriazole 704 gives
R-substitution with respect to benzotriazole upon
alkylation to give 705 and upon reaction with carbonyl
compounds to form products 706. The latter
product cyclizes to furan derivatives 707 (Scheme
132). 364,365
Scheme 132
6. 4H-1,3-Dioxins
Clean reactions of 4H-1,3-dioxin anion 708 with
various alkyl halides, carbonyl compounds and ethylene
epoxide takes place to give 709 which furnishes
upon thermolysis a mixture of the enone 710 and the
enal 711. The 4H-alkyl-1,3-dioxin (709, E) alkyl)
can be deprotonated again and treated with methyl
iodide to give a mixture of three disubstituted dioxins
712, 713, and 714 (Scheme 133). 366,367
Scheme 133
B. Sulfur with Oxygen, Silicon, or Halogen
1. γ-Alkoxyallyl Sulfides (RO−C−CdC−SR)
The γ-alkoxyallyl sulfide anion 717 is alkylated at
the carbon R to the sulfur and γ to the alkoxy group
to give 716. 336,368-370 Such alkylation even occurs R
to the sulfur atom when this is the more hindered
carbon. 371 Furthermore, anion 717 reacts in the
presence of HMPA R to the sulfur with carbonyl
compounds forming 718; enolate trapping with
Ph3SnCl was found crucial for effective R-attack in a
synthesis of prostaglandins. 372 Similarly, an R-selective
attack at the position adjacent to sulfur is
observed in the reaction of 717 with epoxides to give
bishomoallyl alcohols 719 which generate tetrahydropyrans
720 by acid-catalyzed cyclization (Scheme
134). 373
Scheme 134
γ-Selective sulfenylation of 721 gives 722. Subsequent
alkylation of 723 is directed by the methylthio
substituent in anion 723 to give entirely the γ-product
726 with respect to the silyloxy group. Compound
726 was then converted into the enone 725 (Scheme
135). 58