Wilhelm V. Dahlhoff

A Convenient Preparation of Trimethylborane and Triethylborane

Abstract A convenient, high yield preparation of Me3B on a laboratory scale from (n-BuO)3B and Me3Al2Cl3 is described. The preparation of Et3B from Al3Et and Et2O[sbnd]BF3 on a laboratory scale and from AlEt3 and KBF4 on a pilot plant scale are also given.

Amphiphilic Carbohydrate-Based Mesogens, 2 [1] Aldose Di-n-alkyl Dithioacetals: Novel Double-Tailed Thermotropic Liquid Crystals

Mercaptolyses of the pentoses [D-lyxose (1), D-xylose (2), L-arabinose (3)] and hexoses [D-mannose (4), D-glucose (5), D-galactose (6)] with n-alkyl thiols having chain lengths ≥ C6 gives mesogenic aldose di-n-alkyl dithioacetals 7-12.

Synthesis of new chiral macrocyclic polyhydroxy ethers by reduction of cyclodextrins

The new chiral macrocyclic polyhydroxy ethers (5) and (8) were prepared by treatment of β- and α-cyclodextrins with diethylborane and 9-borabicycle[3.3.1]nonan-9-yl methanesulphonate as catalyst.

An isomer-free hexacoordinate bis(acetylacetone)-silicon(IV) complex

Abstract The reaction of diphenyldichlorosilane with acetylacetone in the presence of imidazole yields the known dienolate ( 1 ) and the new stable, isomer-free hexacoordinate silicon complex ( 2 ).

Organoboron-Monosaccharides, XIV Routes to α-and β-D-Mannofuranosyl β-D-Mannofuranosides

Abstract Stereoselective glycosylations of 2,3:5,6-di-O-ethylboranediyl-α-D-mannofuranosyl bromide (1) by two independent routes involving 1-O-tri-n-butyl-stannyl and 1-O-triethylborate α-D-mannofuranosyl derivatives give α-D-mannofuranosyl /β-D-mannofuranoside (8a) after deprotection. β-D-Mannofuranosyl β-D-mannofuranosides can be prepared by reaction of 1 with the sodium triethylborate derivative of 2,3:5,6-di-O-isopropylidene-β-D-mannofuranose (11) and by reacting 1 with hexabutyldistannoxane. The latter approach allows the synthesis of β-D-mannofuranosyl β-D-mannofuranoside (8b) after total deprotection.

Organoboron-Monosaccharides, XIII β-D-Mannofuranosides: Highly Stereoselective Syntheses and NMR Characterization

Abstract Stoichiometric reactions of 2,3:5,6-di-O-ethylboranediyl-α-D -mannofuranosyl bromide (1) with O -nucleophiles at room temperature give β-D-mannofuranosides with excellent stereoselectivities. The labile glycosides obtained are deboronated in quantitative yields and then converted to their tetra-O -acetates. The products are characterized by NMR spectroscopy.

Synthesis of Methyl 6-Deoxy-6-diphenylphosphino-α-D-glucopyranoside: Temperature-Dependence of the Primary O-Tosyl Cleavage Mode

Abstract Methyl α-D-glucopyranoside is converted to methyl 6-p-toluenesulfonyl-2,3,4-tris-O-trimethylsilyl- α-D-glucopyranoside 2 and then reacted with lithium diphenylphosphide in THF. When the reaction is carried out at room tem perature and below, S-O cleavage dominates giving methyl 2,3,4-tris-O-trimethylsilyl-α-D-glucopyranoside 3 , whereas at 60°C in THF or at 35°C in diethyl ether, C-O cleavage occurs yielding the title carbohydrate-phosphine 4 in good yield after deprotection

AMPHIPHILIC CARBOHYDRATE-BASED MESOGENS .10. SYNTHESIS OF MESOGENIC 2-O-N-ALKYL-L-THREITOLS

Dimethyl-L-tartrate 1 is converted into 2,3-O-n-heptylidene-decylidene dimethyl-L-tartrates 2 which are reduced with ethyldiboranes alone and then in the presence of 9-methylsulfonyloxy- 9-borabicyclo[3.3.1]nonane (MSBBN ) to yield 2-O -alkyl-L -threitols 4, after deprotection. The amphiphilic compounds 4 are thermotropic mesogens which display the smectic A liquid crystalline phase on melting.

Synthesis and Stereoselective Glycosylations of 3-O-Acetyl-2,4-O-phenylboranediyl-β-D-ribopyranosyl Bromide

Crystalline 3-O-acetyl-2,4-O-phenylboranediyl-β-D-ribopyranosyl bromide (5) is prepared by an easy four-step synthesis from D-ribose (1), the first three steps of which are realised in an one-pot manner. 5 reacts stereoselectively with sodium methoxide and phenoxide to give the pure methyl and phenyl a-D-ribopyranosides 7 a and 7 b after deboronation and deacetylation.

Stereoselective Syntheses of α-D-Ribopyranosyl Disaccharides [1]

1 → 6-, 1 → 3- and 1 → 1-linked α-D-ribopyranosyl disaccharides 2a, 2b, and 5, respectively are prepared with ≥95% stereoselectivities by reacting 3-O-acetyl-2,4-O-phenylboranediylβ-D-ribopyranosyl bromide (1) with the sodium organooxytriethylborates of 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose, 1,2 : 5,6-di-O-isopropylidene-α-D-glucofuranose and with hexabutyl-distannoxane, respectively. After deboronation and deacetylation 3a, 3b, and 6 are obtained and these are acetylated to give 4a, 4b, and 7.