New synthetic reactions. Sulfenylations and dehydrosulfenylations of esters and ketones

Abstract

Quenching the enolates of esters and ketones with dimethyl disulfide or diphenyl disulfide produces the corresponding a-sulfenylated products. The regio-and chemospecificity of these reactions are defined. Oxidation to the sulfoxide followed by thermolysis leads smoothly to the @unsaturated systems. Temperatures for the elimination of the phenyl sulfoxides are normally around 50 O C , whereas those for the methyl sulfoxides are normally around 110 O C . In both cases, the presence of the carbonyl group significantly facilitates the elimination. Dipole-dipole effects account, in part, for this effect and rationalize the regioselectivity observed in cyclic cases. In some cases, the use of sulfenic acid traps, amines or trimethyl phosphite, is required for good yields. The synthesis of two bee pheromones demonstrates the utility of this approach for introduction of unsaturation. Conditions for mono-vs. disulfenylation are discussed. Use of the latter to effect conversion of an active methylene group into a carbonyl group is illustrated.

Synthesis and some 4+3 cycloaddition chemistry of a sulfur-substituted allylic acetal

“…The N,N-dimethylhydrazone of commercially available dimethoxyacetone (1) was prepared in 90% yield by reaction of the ketone with dimethylhydrazine in ether at 0 o C. 7 Deprotonation of the hydrazone 2 with LDA and trapping with diphenyl disulfide afforded the ketosulfide 3 in 67% yield after hydrolysis of the hydrazone functionality. 8 Reaction of this species with triethylamine and chlorotrimethylsilane afforded the enol ether 4 in 91% isolated yield (Scheme 1). The stereochemistry of 4 was established as shown (Z) by NOESY spectroscopic data, which showed a cross peak between the olefinic hydrogen (5.83 ppm), and the hydrogens of the methoxy group (3.36 ppm).…”

(E)-2-(2-Hydroxyethylidene)-6-methyl-5-heptenal (α-Acariolal) and (E)-2-(2-Hydroxyethyl)-6-methyl-2,5-heptadienal (β-Acariolal), Two New Types of Isomeric Monoterpenes…

“…After protecting the carboxyl group of 6 by (trimethylsilyl)diazomethane and the hydroxy group by tert-butyldimethylchlorosilane, resulting methyl 2-[2-(tert-butyldimethylsilyl)oxy- ethyl]-6-methyl-2-methylthio-5-heptenoate (8) was oxidized with sodium metaperiodate. The resulting sulfoxide (9) was decomposed by re‰uxing in toluene 10) to give a mixture of a and b isomers (10; a:b＝ 1.5:1). DIBAL reduction of both the a and b isomers (10) and subsequent deprotection by using n-Bu 4 NF gave target compounds 1 and 2.…”

Synthesis of dodecahedrane precursors. 3. Synthesis of alkylidene-1,3-cyclopentanediones and attempts to roof peristylanes

“…With this change, the desired pericyclic elimination might be able to compete successfully with the homolytic bond cleavage pathway. The sulfenylation of ketones has generally been achieved by reaction of the ketone enolate with diphenyl disulfide (12). To this end, the potassium enolate of 2-isopropyl-1,3-cyclopentanedione was prepared by reaction with potassium hydride in tetrahydrofuran.…”

“…The crude product (20 mg) was purified by preparative tlc (30% ethyl acetate -methylene chloride). The component at Rf = 0.18 was crystallized from benzene as feathery crystals of tetra01 52 (12 …”