Triethylamine Triple bonds

In the presence of a catalytic amount of triethylamine, a readily enolizable carbonyl compound like acetylacetone (25) can undergo a Michael-type addition onto the triple bond of 23 with C-C bond formation, and subsequent 1,2-addition of the hydroxy group with elimination of an alcohol (MeOH or EtOH) to eventually yield a pyranylidene complex 28 (mode E) [29]. The most versatile access to / -donor-substituted ethenylcarbene complexes 27 is by Michael-type additions of nucleophiles, including alcohols [30-32], primary... 

The reactions of the corresponding propargyl sulfoxides and sulfones now resemble the chemistry of the other acceptor-substituted derivatives such as ketones and aldehydes (see Section 1.2.4). Compared with the thioethers, here much milder bases are sufficient apart from aluminum oxide, often triethylamine or potassium carbonate are used. Sometimes even a spontaneous isomerization takes place. The selective isomerization of one triple bond in the presence of a second triple bond in 126 [313] (Scheme 1.56) or an allyl sulfone in 129 [314] (Scheme 1.57) are just two examples out of a whole series [178, 304, 313, 315-331]. When, on the other hand, the in situ oxidation of 126 was carried out in an aprotic solvent, no isomerization at all was observed. 

Formic acid, anhydrous (M.W. 46.03, m.p. 8.5°, b.p. 100.8°, density 1.22), or a 90% aqueous solution, is an excellent hydrogen donor in catalytic hydrogen transfer carried out by heating in the presence of copper [77] or nickel [77]. Also its salt with triethylamine is used for the same purpose in the presence of palladium [72, 73], Conjugated double bonds, triple bonds, aromatic rings and nitro compounds are hydrogenated in this way. 

Despite the typical use of the 1,5-dienic system in the hetero-Cope rearrangement the participation of triple bonds, C=N and C=C, in the [3,3]-sigmatropic rearrangement was also reported. Synthesis of A-substituted benzimidazolinones 175 by a hetero-Cope rearrangement of the adduct 174 formed by reaction of A-arylhydroxamic acids 172 with cyanogen bromide 173 in the presence of triethylamine and at low temperatures was reported by Almeida, Lobo and Prabhakar (equation 51). 

Intramolecular Heck cyclizations.13 Pd(0)-catalyzed cyclization of substrates containing one alkenyl and one vinyl iodide group is a well-established route to bicyclic products (14, 297-298 15, 301-302). Tandem cyclization to tricyclic products is possible when the substrate contains a triple bond. Thus, in the presence of a Pd(0) catalyst and 2 equiv. of triethylamine, 1 undergoes tricyclization to 2 in high... 

The rather unusual precatalyst silver(i) isocyanate was found to efficiently catalyze the cyclization of propargyl carbamates 420 to 4-alkylideneoxazolidin-2-ones 421 in good to high yields (Scheme 123).348 The presence of a base such as potassium /-butoxide or triethylamine is required for formation of the amide nucleophile which undergoes a stereoselective intramolecular attack at the activated triple bond (/rstereo-isomer 421 exclusively. Likewise, homopropargyl carbamates are converted into six-membered (Z)-4-alkylidene-l,3-oxazinane-2-ones under the same conditions. 

Phenylpropiolic thioanilide and bromonitromethane in presence of triethylamine give the 2-nitrothiophene 24.22 Evidently, initial 5-alkylation is followed by addition of the acidic methylene to the triple bond as in Eq. (5). 

A radical diphosphanylation of alkynes using tetraorganodiphosphanes as precursors for phosphanyl radicals has been applied to the synthesis of a doubly phosphinated diene 200 (Scheme 2.37)7 Tetraphenyldiphosphane was generated in situ from diphenylphosphane with an excess of chlorodiphenylphosphane in the presence of triethylamine. Addition of the phosphanyl radical to one C = C triple bond in the dialkyne 199 leads to vinyl radical 201, which undergoes a 5-exo cyclization (out of a Z-configured vinyl radical to minimize sterical hindrance in the cyclization) to give vinyl radical intermediate 202. The latter is trapped by a second phosphine moiety in a radical substitution step. The radical cyclization product is ultimately isolated as bis-phosphane sulfide 200 after treatment of the intermediate phosphane 203 with sulfur. 

Mechanistically, this new insertion-CI-Diels-Alder hetero domino sequence can be rationalized as follows (Scheme 64) After the oxidative addition of the aryl halide 115 or 118 to the in situ generated Pd(0) species the arylpalladium halide 120 intramolecularly coordinates and inserts into the tethered triple bond via a syn-carbopaUadation to furnish cyclized vinylpalladium species 121 with a p-acceptor substitution in a stereospecific fashion. Transmetallation of the in situ generated copper acetylide 122 gives rise to the diorganylpalladium complex 123 that readily undergoes a reductive elimination and liberates the electron poor vinylpropargylallyl ether 124. The triethylamine catalyzed propargyl-allene isomerization furnishes the... 

Reduction of azides. Alkyi and aryi azides are reduced to primary amines by the combination of 1,3-propanedithiol and triethylamine (equation 1). The method is highly selective, and does not affect double or triple bonds, nitro, nitrile, carboxylic acid, amide, and ester groups. ... 

Semihydrogenation of alkynes. Formic acid is a hydrogen source for the Pd(0)-catalyzed transfer reduction of the triple bond to afford the (Z)-alkene with a selectivity of 89-98%. The reducing system also contains triethylamine. 

Preparative Methods most often prepared (eq 1) by pyrolysis of ethoxy(trimethylsilyl)acetylene at 120 °C (100 mmol scale, 65% yield). Recently, pyrolysis of t-butoxy(trimethylsilyl) acetylene has been shown to be a convenient alternative for the preparation of trimethylsilylketene (1). Thermal decomposition of t-butoxy(trimethylsilyl)acetylene causes elimination of 2-methylpropene slowly at temperatures as low as 50 °C and instantaneously at 100-110 °C (30 mmol scale, 63% yield). The main advantage of this method is that it is possible to generate trimethylsilylketene in the presence of nucleophiles, leading to in situ trimethylsilylacetylation (eq 2). Increased shielding of the triple bond prevents problems such as polymerization and nucleophilic attack that occur when the ketene is generated in situ from (trimethylsilyl)ethoxyacetylene. Trimethylsilylketene can also be prepared (eq 3) via the dehydration of commercially available trimethylsilylacetic acid with 1,3-dicyclohexylcarbodiimide (DCC) in the presence of a catalytic amount of triethylamine (100 mmol scale, 63%). Other typical methods used for ketene generation such as dehy-drohalogenation of the acyl chloride and pyrolysis of the... 

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