Triethylamine complexes

Borane—triethylamine complex (4) is used when slow Hberation of borane at elevated temperatures is advantageous, eg, in the cycHc hydroboration of trienes to avoid the formation of polymers (59). 

R = H, X = S, A = Et3N and Py). In solution the former is mainly in an ionic form the latter exists as a complex. The basicity of the amine is assumed to be important. Triethylamine is a stronger base than pyridine and the ionic form is stabilized. When the proton affinity is weak, the basicity in relation to the B(III) atom, a Lewis acid, plays an important role. This involves an equilibrium shift toward the complex. This assumption is confirmed by an easy displacement of pyridine by triethylamine. The reverse process demands more severe conditions. In the NMR spectra of the triethylamine complex the signal is shifted from 22 to 42 ppm as pyridine is added. The absence of signals of two separate forms is evidence in favor of their fast interconversion. The chemical shift of the signal in 3IP spectra is 22 ppm (EtOH), 26 ppm (Py, DMFA), and 42 ppm (EtOH, Py) for complexes with triethylamine and pyridine. 

Meerwein and co-workers113. 1141 have also studied the addition of diethyl ether, pyridine, and triethylamine complexes of Ixm.n trifluoride to epichlorohydrin and ethylene oxide. Once more, inner oxonium salts were ieolable from the reactions, and could bepuriiicd and characterised by further transformations. 

Methyl perfluoromethacrylate reacts with allyl and propargyl alcohols to give the Michael addition products 19 and 20, respectively these eliminate hydrogen fluoride in the presence of the boron trifluoride-triethylamine complex and rearrange to acyl fluorides 21 and 22. Hydrolysis of the acyl fluorides with base results in decarboxylation to give the 2-(trifluoromethyl) esters 23 and 24.11... 

In order to prevent competing homoallylic asymmetric epoxidation (AE, which, it will be recalled, preferentially delivers the opposite enantiomer to that of the allylic alcohol AE), the primary alcohol in 12 was selectively blocked as a thexyldimethylsilyl ether. Conventional Sharpless AE7 with the oxidant derived from (—)-diethyl tartrate, titanium tetraisopropoxide, and f-butyl hydroperoxide next furnished the anticipated a, [3-epoxy alcohol 13 with excellent stereocontrol (for a more detailed discussion of the Sharpless AE see section 8.4). Selective O-desilylation was then effected with HF-triethylamine complex. The resulting diol was protected as a base-stable O-isopropylidene acetal using 2-methoxypropene and a catalytic quantity of p-toluenesulfonic acid in dimethylformamide (DMF). Note how this blocking protocol was fully compatible with the acid-labile epoxide. 

Removal of the TBDPS ether in intermediate 71-1 en route to Myxovirescin A1 [Scheme 4.71] gave the desired alcohol 71.2 along with the acyl migration product 71 3.126 With TBAF, a 1 1 mixture of 71,2 and 71,3 was obtained but the rearrangement was minimised to 10% using the hydrogen fluonde-triethylamine complex at room temperature. 

The 5 (or 6) hydrogen fluoride/triethylamine complex can also be used as a mild and selective hydrofluorination agent for preparing tertiary alkyl fluorides. ... 

Hydroboration. Thexylborane stabilized as the triethylamine complex is not useful for hydroboration, because 2,3-dimethyl-2-butene is displaced with formation of RBH2-N( 2145)3. However, TBDA is a useful reagent for hydroboration and for various reductions. Thus it reacts with 1-octene to form di- -octylthexylborane in quantitative yield. It is comparable to thexylborane-THF for reduction of aldehydes and ketones. Carboxylic acids are reduced to the corresponding alcohol. 10-Undecenoic acid is reduced selectively to undecanoic acid (90% yield). Tertiary amides are reduced very rapidly to f-amines. Acid chlorides and nitriles are reduced very slowly. 

Preparation. The reagent is prepared by the reaction of sodium hydride with N-carbomethoxysulfamoyl chloride (2, see Methyl N-sulfonylaetiiane triethylamine complex, this volume). This precursor is treated with sodium hydride and acetonitrile NaH... 

MethyI-l-pheuyl-.3-phospholanc oxide, I, 695 2, 279. Supplier Eastman. Methyl N-sulfonylnrethane triethylamine complex,... 

The laser-initiated polymerization of styrene with maleic anhydride has been said to occur through either a singlet or triplet excimer (the authors surely mean exciplex ) of the anhydride as shown in Scheme 4. This study provides an interesting comparison between laser- and u.v.-initiated polymerization, and Table 2 shows clearly that the former is a very energy-efficient system. In the laser-initiated polymerization of a thiol-ene system, oxygen inhibition was not a significant problem and similar conclusions were reached on the energy efficiency of lasers. On a related note, the efficiency of the well-known benzo-phenone-triethylamine complex is apparently enhanced if carboxylic acids are added to the system. ... 

Aminosugar-derived glycal 141 was obtained by this method from an appropriate chiral precursor 139 [237], Unexpectedly, however, reaction of tungsten intermediate 140 with tri- -butyltin triflate and triethylamine in ether gave the glycal 141 (in 85% yield) instead of the 1-stannyl derivative (O Scheme 47). The molybdenum carbonyl-triethylamine complex afforded the same product, although in a much lower yield. 

URETHANES Diphenylphosphoryi azide. Methyl N-sulfonyl urethane triethylamine complex. 

Methyl sulfonates, 340 Methyl N-sulfonylurethane, 332-333 Methyl N-sulfonylurethane triethylamine complex, 343-344... 

DEHALOGENATION Diiron nonacarbonyl. Lithium amalgam. Phenanthrene-Sodiiim. Sodium thiosulfate. Triethyl phosphite. DEHYDRATION Alumina. Boron trifluo-ride n-butyl etherate. Dimethyl sulfoxide. Hexamethylphosphoric triamide. Iodine. Methyl N-sulfonylurethane triethylamine complex. Phosphonitrilic chloride. Thio-nyl chloride. Triphenylphosphite methio-dide. 

TABLE 22. Solvent effect on the PT in 2,4, 6-trichlorophenol -triethylamine complexes ... 

Hydroboration of acyclic trienes with 1 1 H3B THF at 0°C leads to insoluble products. Monomeric bicyclic boranes are produced in low yields. These organoboranes are obtained, however, either by thermal treatment of the insoluble products or directly by hydroboration of trienes with borane-triethylamine complex . ... 

Borane-triethylamine complex proceeds similarly as a hydroborating agent. Low concentration of borane in the mixture provided by slow thermal dissociation of the complex is advantageous in these hydroborations facilitating the formation of cyclic products . 

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