Synthesis of glycoconjugate fragments of mycobacterial phosphatidylinositol mannosides and lipomannan

• Benjamin Cao,
• Jonathan M. White and
• Spencer J. Williams

Beilstein J. Org. Chem. 2011, 7, 369–377, doi:10.3762/bjoc.7.47

• %). Orthoesters are common by-products of glycosylation reactions and typically rearrange under acidic conditions to give trans-linked glycosides [43]. Thus, 14 and 16 were treated with 0.25 equiv of an alternative Lewis acid, TMSOTf, and allowed to react for a longer time to allow the intermediate orthoester to

• isomerize. Under these conditions the disaccharide 26 was isolated in an improved yield of 63%. Also isolated was a 6-O-trimethylsilyl ether (6%), resulting from the reaction of alcohol 14 with TMSOTf. Better still, treatment of 14 and 16 with 0.25 equiv of BF3·Et2O afforded 26 in 76% yield. A similar

Addition of lithiated enol ethers to nitrones and subsequent Lewis acid induced cyclizations to enantiopure 3,6-dihydro-2H-pyrans – an approach to carbohydrate mimetics

• Fabian Pfrengle and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2010, 6, No. 75, doi:10.3762/bjoc.6.75

• , even after prolonged reaction times. The reactions with stoichiometric amounts of TMSOTf gave monocyclic, bicyclic, and spirocyclic dihydropyrans depending on the 1,3-dioxolanyl-substituted enol ether employed (Table 2). Unfortunately, attempts to generate an eight-membered (or six-membered) ring by

• -type cyclization. Thus, 2-lithiofuran was added to nitrone 2a [18] and then protected with TBSOTf to give hydroxylamine derivative syn-4f in 55% (Scheme 4). Remarkably, subsequent treatment with 2 equiv of TMSOTf did not lead to the desired bicyclic product. Since no conversion was observed, the lower

• respective 1,3-dioxolanyl-substituted enol ether (1 equiv) in CH2Cl2 (6 mL/mmol) at −30 °C, was added TMSOTf (2 equiv) and the resulting solution stirred until it slowly reached room temperature (6 h). The reaction was quenched by the addition of water. After separation of the layers, the aqueous phase was

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

• turn the α-directing participating group into an anomeric leaving group reactive enough to partake in glycosylations. Thioglycosides are widely used as glycosyl donors [14][15], and many different reagents are available for their activaton including N-iodosuccinimide (NIS)/TMSOTf [16], dimethyl

Acid- mediated reactions under microfluidic conditions: A new strategy for practical synthesis of biofunctional natural products

• Katsunori Tanaka and
• Koichi Fukase

Beilstein J. Org. Chem. 2009, 5, No. 40, doi:10.3762/bjoc.5.40

• method [27]. For the present microfluidic sialylation, a propionitrile solution of sialyl donor 1a and acceptor 2 with various concentrations was mixed with TMSOTf solution in dichloromethane at −78 °C using an IMM micromixer [42] with a channel width of 40 μm at a flow rate of 1.0 mL/min (Table 1

• , acceptor 2, and TMSOTf were adjusted to 0.15 M, 0.1 M, and 0.08 M, respectively, disaccharide 3a was obtained in only 14% yield and a large amount of the acceptor 2 was recovered (entry 1). However, we were pleased to find that the yield of 3a dramatically increased (88%) when the concentration of the

• severe problem under such drastic conditions [41]. The use of excess amounts of donor 1a and/or TMSOTf in batch reaction did not improve the sialylation yield, but rather resulted in a large amount of glycal production. Apparently, the efficient micromixing between substrates and the high concentration

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

Tether- directed synthesis of highly substituted oxasilacycles via an intramolecular allylation employing allylsilanes

• Peter J. Jervis and
• Liam R. Cox

Beilstein J. Org. Chem. 2007, 3, No. 6, doi:10.1186/1860-5397-3-6

• precursors in hand, we were ready to conduct our intramolecular allylation study. Each aldehyde substrate (>95:5 d.r. in all four cases) was treated with TMSOTf in the presence of 2,4,6-tri-t-butyl pyrimidine (TTBP), [24] which acts as a Brønsted acid scavenger, in CH2Cl2 as solvent, conditions that had

The oxanorbornene approach to 3-hydroxy, 3,4-dihydroxy and 3,4,5-trihydroxy derivatives of 2-aminocyclohexanecarboxylic acid

• Ishmael B. Masesane,
• Andrei S. Batsanov,
• Judith A. K. Howard,
• Raju Mondal and
• Patrick G. Steel

Beilstein J. Org. Chem. 2006, 2, No. 9, doi:10.1186/1860-5397-2-9

• or various trapping agents (e.g. TMSCl, TMSOTf) were partially successful, albeit only on very small scale, the use of a less coordinating potassium counterion (KHMDS) allowed the isolation of the dihydroanthranilate esters 4 and 5 in 71% and 69% yield respectively together with variable amounts of