Benzyne arylation of oxathiane glycosyl donors

• Martin A. Fascione and
• W. Bruce Turnbull

Beilstein J. Org. Chem. 2010, 6, No. 19, doi:10.3762/bjoc.6.19

• then already pre-organised to give a 1,2-cis directing group upon activation, and afford 1,2-cis-glycosides 7 on alcohol addition. Following the synthesis of the oxathiane ketal glycosyl donors 5, activation of the β-thioglycoside linkage was necessary to form the key trans-decalin sulfonium ion 6, and

• (methylthio)sulfonium trifluoromethanesulfonate (DMTST) [17][18], PhSeOTf [19], MeS-SMe/Tf2O [20], and MeOTf [21][22][23]. However, in order to recreate the reactive sulfonium ion used by Boons, it would be necessary to activate the anomeric sulfur with a phenyl group. Herein we describe our synthetic

• phenyl sulfonium ion 20, followed by glycosylation of the acetate anion. The very high α-stereoselectivity (α:β > 98:2) of the reaction was in line with selectivities previously observed for intermediate oxathiane sulfonium ions [13]. When the reaction was repeated in the absence of 1-ABT, the starting

Enantiospecific synthesis of [2.2]paracyclophane- 4-thiol and derivatives

• Gareth J. Rowlands and
• Richard J. Seacome

Beilstein J. Org. Chem. 2009, 5, No. 9, doi:10.3762/bjoc.5.9

• mediated by a sulfonium salt has recently been divulged [16]. The only reported synthesis of enantiomerically pure [2.2]paracyclophane-4-thiol entails the palladium-mediated addition of triisopropylsilanethiol to a triflate formed from previously resolved (R)-4-hydroxy[2.2]paracyclophane [18]. We are

Synthesis of new C^α-tetrasubstituted α-amino acids

• Andreas A. Grauer and
• Burkhard König

Beilstein J. Org. Chem. 2009, 5, No. 5, doi:10.3762/bjoc.5.5

• sulfonium salt 1 and an aldehyde. Applying strongly basic conditions leads to the abstraction of the α-proton of the methionine, the aldehyde undergoes nucleophilic attack by the ester enolate and the displacement of the sulfonium salt substituent by the alkoxy group gives the target TAA. To avoid undesired

• (see Scheme 1). Therefore different bases (namely KOH, KOt-Bu and CsOH) and also different equivalents of sulfonium salt 1, aldehyde and base were screened to find the optimal conditions for the TAA synthesis. In all cases, dry acetonitrile was used as solvent, and the temperature was kept at −6 °C to

• sulfonium salt 1 was increased with respect to the aldehyde and the optimal amount of base was investigated. The highest yields of TAA were obtained with identical amounts of base and sulfonium salt. To optimize the ratio of aldehyde to sulfonium salt 1, reactions with ratios of 1:1.5, 2:1 and 8:1 aldehyde

Synthesis of methylenebisamides using CC- or DCMT- activated DMSO

• Qiang Wang,
• Lili Sun,
• Yu Jiang and
• Chunbao Li

Beilstein J. Org. Chem. 2008, 4, No. 51, doi:10.3762/bjoc.4.51

• amides can be aromatic or aliphatic. The operation is simple and the reagents are inexpensive. Keywords: amides; condensation; DMSO; methylenebisamides; 2,4,6-trichloro[1,3,5]triazine; Introduction Sulfoxides are activated by electrophiles to produce reactive sulfonium salts. These electrophiles

• include DCC [1][2], acetic anhydride [3], trifluoroacetic anhydride [4], acetyl chloride [5], phosphorus pentoxide [6], polyphosphoric acid [7], sulfuric acid and sulfur trioxide [6] etc. A few reactions such as the Pummerer reaction [8] and Swern oxidation [9] can be performed via the reactive sulfonium

• on the chlorination [10] and etherification [11] of benzyl alcohols and from other references [12][13][14], we believe the reaction between 2,4,6-trichloro[1,3,5]triazine (cyanogen chloride, or CC) and DMSO produces a reactive sulfonium salt intermediate. Therefore, it was of interest to study the

Trifluoromethyl ethers – synthesis and properties of an unusual substituent

• Frédéric R. Leroux,
• Baptiste Manteau,
• Jean-Pierre Vors and
• Sergiy Pazenok

Beilstein J. Org. Chem. 2008, 4, No. 13, doi:10.3762/bjoc.4.13

• hypofluorite (FOCF3) to olefins [38]. The introduction of the trifluoromethoxy substituent into carbohydrates was realized using tris(dimethylamino)sulfonium trifluoromethoxide (TASOCF3) as OCF3-transfer reagent [39]. This compound can be prepared by reaction of carbonyl fluoride with tris(dimethylamino

• )sulfonium difluorotrimethylsilicate in anhydrous THF at −75 °C (Scheme 9) [40]. The trifluoromethoxide anion is a relatively poor nucleophile. However, when reacted with primary triflate esters of carbohydrates, the anion displaced the triflate under mild conditions. However, although aromatic

• . The stable tris(dimethylamino)sulfonium (TAS) trifluoromethoxide (see Scheme 9 for structure) [40] represents an extreme case. The three carbon-fluorine bonds are stretched by approximately 0.07 Å and the carbon-oxygen bond contracted by 0.09 Å relative to trifluoromethanol [40] and by 0.21 Å relative

Reagent controlled addition of chiral sulfur ylides to chiral aldehydes

• Varinder K. Aggarwal and
• Jie Bi

Beilstein J. Org. Chem. 2005, 1, No. 4, doi:10.1186/1860-5397-1-4

• of the two enantiomers of the chiral benzyl sulfonium salt 1 with glyceraldehyde acetonide were studied in detail. Of the two new stereogenic centers created, it was found that the C1 stereochemistry was largely controlled by the reagent, whereas control at the C2 center was dependent on the aldehyde

• establish the extent of reagent and substrate control in such systems and chose glyceraldehyde 3 as the substrate (Scheme 3, Scheme 4). Results and Discussion The reaction of glyceraldehyde acetonide 3 with the achiral sulfonium salt in the presence of the P2 base (P2 = N,N,N',N'-tetramethyl-N"-[tris