With diethylaminopropyne

In contrast, soft carbon nucleophiles attack at C5. The reaction of 23 with diethylaminopropyne yields alkenyl(amino)pentatetraenylidene complexes (34) by insertion of the C = C bond of the alkyne into the C4=C5 bond of the pentatetrae-nylidene ligand [9]. The reaction is initiated by a nucleophilic attack of the ynamine at C5 followed by ring closure and electrocyclic ring opening (Scheme 3.34). Complexes 34 are obtained as mixtures of s-cis/s-trans isomers. 

Vinyl isocyanate reacts with diethylaminopropyne to give the [4+2] cycloadduct 495 plus 496 as a byproduct. The latter is formed by a [2+2] cycloaddition, followed by... 

Allenes of the type (171) have been prepared by cycloaddition of ynamines with carbon dioxide. The reaction with diethylaminopropyne is complete in one hour at —60 °C and the only contaminant is a small quantity of the aminocyclobutenone (172). 

Since 1,3-dipolar cycloadditions of diazomethane are HOMO (diazomethane)-LUMO (dipolarophile) controlled, enamines and ynamines with their high LUMO energies do not react (79JA3647). However, introduction of carbonyl functions into diazomethane makes the reaction feasible in these cases. Thus methyl diazoacetate and 1-diethylaminopropyne furnished the aminopyrazole (620) in high yield. 

The cycloaddition reaction of 1,2,4-tiiazines 7V-oxides proceeds differently from the reaction of the corresponding 1,2,4-tiiazines. Thus the 1,2,4-triazine 4-oxide 55 acts only as a diene in the reaction with 1 -diethylaminopropyne to afford 2-methyl-4-(dimethylamino)pyrimidines 111. At the same time the 1,2,4-triazine 4-oxides 55 react with l-(dimethylamino)-l-ethoxyethylene by 1,3-dipolar cycloaddition to give 5-methyl-1,2,4-tiiazines 112 (78CB240). 

The formation of a formal [3+2] cycloaddition product 56 upon reaction of the ethoxystyryltungsten complex 53 with 1-diethylaminopropyne, as observed... 

Benzoisothiazole dioxides undergo [2+2] cycloaddition with 1-diethylaminopropyne followed by ring expansion to give 3-diethylamino-l,2-benzothiazepine 1,1-dioxides (378 R1 = Me, R = Et) (76H(5)95). JV-Tosylsulfimines, e.g. (386), are converted into 1,2-benzothiazepines (388) in high yield when treated with triethylamine in benzene under reflux. In the absence of base the intermediate (387) can be isolated (80JCS(Pl)2830, 81JCS(P1)1037). 

Addition of diethylaminopropyne to C60 resulted in a [2+2] cycloadduct that can be ring-opened under acidic conditions, while, when followed by oxidative cy-clization in the presence of activated carbon, novel fullerene lactones were formed [62]. Further work on the reaction of C60 with propiolates in the presence of triph-enylphosphine resulted in the construction of bismethanofullerenes and a [2+2] cycloadduct consisting of a cyclobutane ring fused to a 6,6 ring junction [63]. 

Phenacylpyridinium methiodide, when treated with hydrazine under WolfF-Kishner reduction conditions, is transformed into 6-phenyl-4-propylpyridazine. Some related pyridazines were prepared in a similar manner, but 3-benzoylpyridinium methiodide failed to react [80JCS(P1)72]. 2-Dimethylamino-5-phenyl-l, 3,4-thiadiazin-6-one reacts with the electron-rich 1-diethylaminopropyne to give two pyridazines, 49 and 50, in 72% and 2% yield, respectively. The formation of both compounds is explained by the initial addition of ynamine, ring opening, and cyclization in two ways (82CC1003). 

The reactions of mono-, di-, tri-, and tetramethoxycarbonylpyrazines with 1-diethylaminopropyne (Et NCsCMe) leads to pyridine derivatives (629) and irradiation of the Af-ethoxycarbonyliminopyrazinium ylide (40) with a 100-W high-pressure Hg lamp (Pyrex) gave the A -ethoxycarbonylpyrazole (41) and the parent pyrazine (42) (1248). 

The use of acyl azides in this reaction is not so straightforward. 1-N,N-Diethylaminopropyne (MeC=CNEt2) reacted conventionally with ethyl... 

Diazines, triazines, and tetrazines react with electron-rich dienophiles as well as with electron-deficient dienophiles by a (4- - 2)-cycloaddition reaction. The reaction between 1,2,4-triazines and JV,N-diethylaminopropyne does not give pyridazines as reported previously/ but the corresponding pyrimidines. 

The preparation of pyridazines by cycloaddition of ynamines to 1,2,4,5-tetrazines, followed by extrusion of nitrogen, has been described. However, when 1-diethylaminopropyne reacted with l,2,4,5-tetrazine-3,6-dicarboxamides (27 = 4, 5) besides the corresponding pyridazines (28), almost equal amounts of the new tetrazines (29) were also obtained. These are formed by addition of the ynamine across the amide carbonyl. 

In the last decade new reactions have been elaborated in which pyridazines can be transformed into a variety of other heterocycles. Esters of pyridazine-carboxylic acids and 1-diethylaminopropyne undergo cycloaddition reactions with inverse electron demand. The orientation of the two reactants depends on the position of the carboxylate group in the pyridazine ring. For example, from methyl pyridazine-4-carboxylate the pyridine derivative 245 was formed via the adduct 244 and subsequent elimination... 

A jA -Diethylaminopropyne reacts with A -benzoylisocyanate to give the l,3-oxazin-4-one (174) as the only product. However, although l,3-oxazine-4-thiones (175) are available by the same route, using A -aroylisothiocyanates instead of A -benzoylisocyanate, mixtures result and the oxazine-4-thiones are accompanied by their 2- and 6-isomers (Scheme 48) <86JCR(S)40>. 

Mesomeric betaines (e.g., (158)) undergo 1,4-dipolar cycloadditions with various electron-rich dienophiles thus, with l-A, A -diethylaminopropyne, for example, the adduct (159) is obtained. When heated this expels carbonyl sulfide to generate a-pyridone (160) (Scheme 28) <93TL5408>. 

Cycloaddition of diazo-diazoles and -triazoles with electron-rich dipolarophiles such as 1-diethylaminopropyne affords azolo-l,2,4-triazines. However, these fused products lie outside the scope of this chapter. 

The 2,6-diamino-4//-l,3-selenazine (133) is synthesized by heating the 1,2,4-diselenazole (132) with 7V,7V-diethylaminopropyne at 50-70 °C. Under these conditions ring expansion occurs with... 

Pyrazoles, - Formation. A mixture of the pyrazoles (242) and (243) is produced by thermolysis of the azines PhCH=CHCH=NN=CMeCH=CHAr. The reaction of diazodibenzoylmethane with 1-diethylaminopropyne,... 

A practical and general strategy towards such heterocycles from penam precursors was recently disclosed [129, 130] (Scheme 73). Hydroxamic acids 249, formed by cleavage of the P-lactam ring of the penicillinates 248 with hydroxylamine, underwent a smooth Lossen rearrangement in the presence of A/, iV-diethylaminopropyne. The isocyanate intermediates 250 immediately cyclised to give the desired compounds 251 without racemization. 

Fused 2-methylbutenolides have been prepared in good yield by the addition of 1-diethylaminopropyne to cyclic a-epoxy-ketones (Scheme 21). The intermediate unsaturated amide can by cyclized to the hydroxy derivatives (69) simply by treatment with acid. Alternatively, prior reaction with BF3 followed by acid leads to the unsaturated analogue (70), whereas final reduction with borohydride gives the... 

Addition of ynamines to electron-deficient olefins has been used to prepare cyclobutenes. Ficini, Eman, and Touzin have investigated the [2+2] cycloaddition to AW-diethylaminopropyne to 4-methylcyclohexenone. The reaction was stereoselective, and gave the isomeric adducts (93) and (94) in a 9 1 ratio. Acid hydrolysis of the adducts gave the substituted cyclohexanone (95). Reaction of the ynamine with 1-cyanocyclopentene, catalysed by magnesium bromide, gave the cyclobutene (96). Hydrolysis of (96) with acetic acid gave almost exclusively the cyclobutanone (97). Hydrolysis with hydrochloric acid gave a 20 80 mixture of (97) and its epimer (98). 

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