Cycloaddition, of ynamine with

Cycloaddition of ynamines with sulfenes (generated from sulfonyl chlorides) to give thiete sulfones 132 and 133 has been reported by Truce et (Eq. 21). Acid hydrolysis yields the corresponding enols (134). Other compounds that have been prepared in this manner are 135 and 136. Sulfene... 

The exception to this generalization is the cycloadditions of ynamines with 1,2,4-traizines where the C-5/N-2 cycloaddition process is generally observed [Eq. (27)].93... 

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). 

The cycloaddition of ynamines with aP-unsaturated nitriles gives cyano-aminocyclobutenes (171), which may be isomerized to the more stable (172) when Both (171) and (172) are hydrolysed under acidic conditions... 

Cycloadditions of ynamines to nitroalkenes, 1-Nitrocyclopentene condenses with ynamine 1 in the expected manner (5, 219 7, 107-108) to afford cyclobutene 2 in 40 Xi yield. This reaction is not general, however, since nitroalkencs 3 and 4... 

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. 

Exceptions to this generalization are restricted to the reactions of ynamines with electron-deficient 1,2-diazines, where both C-3/C-6 and C-4/N-l 1,2-diazine cycloaddition have been observed [Eq. (15)].73... 

A similar reaction of a cyanoynamine with phenylsulfene also gave the four-membered cyclic sulfone (equation 93)205. Formation of the four-membered sulfones from cycloaddition of ynamines-sulfenes is again proposed to occur through a zwitterionic intermediate205. 

Phenylthio)mtromethane has been dehydrated and the resultant phenylthionitrile oxide trapped with alkenes to provide isox-azohnes (eq 10). These compounds are convenient precursors for 3-(phenylsulfonyl)isoxazolines and -hydroxy ketones. The cycloaddition-H ing contraction of ynamines with 1-nitro-l-phenylthioalkenes has been used to prepare cyclic nitrones (eq 11)."... 

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. 

On the other hand, the known facts point to an alternative interpretation. The stereochemical course of the reaction may be explained in terms of a polar [2s + 2s] cycloaddition15 which is observed in reactions between very electron-poor and very electron-rich alkcnes. Namely, polar [2 + 2] cycloadditions usually proceed with high regioselectivity ( head to head ) and stereoselectivity under mild conditions33 35. This mechanism is also supported by the fact that a closely related reaction (between an ynamine and iminium salts) passes through a cyclic 4-membered intermediate36, which is probably the result of a polar [2 + 2] cycloaddition (see refs 10 and 37). 

The various transitions of triafulvenes to pentafulvenes achieved by addition of electron-rich double bonds is complemented by the reaction of triafulvenes with ynamines and yndiamines299, which gives rise to 3-amino fulvenes 539. This penta-fulvene type deserves some interest for its merocyanine-like inverse polarization of the fulvene system and its formation is reasonably rationalized by (2 + 2) cycloaddition of the electron-rich triple bond to the triafulvene C /C2 bond (probably via the dipolar intermediate 538) ... 

Group 6 allenylidenes also react with the carbon-carbon triple bond of ynamines to yield similar cyclobutenylidene derivatives 88 along with the corresponding alkenyl-aminoallenylidenes 89 (Scheme 32) [286]. These aminoallenylidene complexes result from a formal [2-1-2] cycloaddition between the ynamine C=C and allenylidene Cp=Cy bonds followed by cycloreversion. A stepwise cyclization initiated by the addition of the nucleophilic R C=CNEt2 carbon at the C or Cy position has been proposed in the formation of these isomeric products. As commented previously, unlike their Cr and W counterparts, the reactions of... 

Nitrooxazoles 271a-C also react with electron-rich ynamines to yield isoxazo-lines. °° The proposed reaction mechanism involves the Michael addition of the ynamine to give 275, followed by rearrangement to a nitrile oxide 277. Intramolecular 1,3-dipolar cycloaddition of 277 accounts for the exclusive cis stereochemistry observed in the products 278a-c (Scheme 8.78). 

Some examples dealing with the [4 + 2] cycloaddition of ketenimines have been recorded (Scheme 58). Thus, thioketones and ynamines reacted with N-aryl ketenimines 257 through the carbon—nitrogen and the conjugated aromatic carbon—carbon double bonds to yield benzothiazine derivatives 258 (80JOC3766 82JOC3998) and substituted quinolines 259 (73JA5417), respectively. Simple ketenimines 261 were formed by reaction... 

Another well-studied cycloaddition of 1,2,4-triazines is the reaction with ynamines (423). In this the dienophile often attacks the 1,2,4-triazines across the 2- and 5- rather than the 3- and 6-positions. This can perhaps be due to the transition state of the cycloaddition with ynamines being more polar than that in the cycloaddition with alkenes, and a partial negative charge in the 1,2,4-triazine ring is better stabilized at a nitrogen (N-2) than at a carbon (C-6). The products isolated from these reactions are pyrimidines (424). It was shown by using lsN-labelled 3-methyl-l,2,4-triazine that the reaction is in fact a [4 + 2] cycloaddition to N-2 and C-5 and not a [2 + 2] cycloaddition to the N(4)—C(5) bond (72LA(758)125). 

By analogy with the formation of dihydropyrans from unsaturated carbonyl compounds and alkenes (see Section 2.24.2.7.l(i)), the synthesis of 4//-pyrans from the [4 + 23-cycloaddition of unsaturated carbonyl compounds and alkynes would seem to offer some potential. Such a reaction has indeed proved of value, but examples are largely restricted to the use of ynamines as the dienophile (76BSF987). 

Catalyst for DIels-Alder reaction of ynamlnes. A zero-valent iron species prepared by reduction of iron(III) chloride with isopropylmagnesium chloride serves as a unique catalyst for cycloaddition of butadiene and ynamines (1) to form 1,4-cyclohexadienamines (2). These products are hydrolyzed by mild acid treatment to (3,y-cyclohexenones (3), which are isomerized to either 4 or 5 by catalytic amounts of rhodium catalysts. 

Diarylcyclopropenones reacted with ynamines in refluxing toluene to give cyclopentadienones 1 in a [2 + 3] cycloaddition of the ynamine to the single bond of the cyclopropenone. ... 

The cycloaddition of l-methoxy-3-trimethylsilyoxy-1,3-butadiene with 3-methyl-1,2-benziso-thiazole 1,1-dioxide (107) (R = Me) affords the pyridone (108) <84H(22)67l>. An improved synthesis of 1,2-benzisothiazole 1,1-dioxide has led to the preparation of the benzothiazepine (109) (R = H) by cycloaddition of the ynamine followed by ring expansion <83CC520>. Addition of yV,7V-diaikylprop-l-ynamines to 3-substituted 1,2-benzisothiazole 1,1-dioxide (107) (R = SMe, SPh, SePh) gives mainly the imine-vinylamine (110) with only small amounts of the benzothiazepine (109) <85CC845>. 

Cycloaddition of diazoazoles, such as 2-diazoimidazole, 3-diazopyrazole, 3-diazo-l,2,4-tria-zole, 4-diazo-l,2,3-triazole, 3-diazoindazole, 3-diazopyrazolo[5,4-fr]pyridine or 3-diazopyra-zolo[5,4-c]pyridazine, with electron-rich dipolarophiles (dienophiles), such as 7V,7V-diethylprop-1-ynamine, affords azolo-l,2,4-triazines 15, aromatic lOn-systems.326a c... 

Triethyl l,3,5-triazine-2,4,6-tricarboxylate and 2,4,6-tris(methylsulfanyl)-1,3,5-triazine react in an inverse electron demand Diels-Alder reaction with several electron-rich dienophiles.6 The tricarboxylate 9 (R1 = C02Et) undergoes a well-defined [4 + 2] cycloaddition reaction with ynamines and enamines. In the case of ynamines, the [4 -1- 2] cycloaddition is followed by a retro Diels - Alder reaction at 40 100 °C with direct formation of the substituted pyrimidines 11. In the case of enamines, the cycloaddition provides stable, isolable [4 + 2] adducts 12. The subsequent retro Diels-Alder reaction and the final aromatization step is catalyzed by a mixture of hydrochloric acid and dioxane, anhydrous p-toluencsulfonic acid or acetic acid. This two-step process can be reduced to a single operation by conducting the reaction in a solution of dichloromethane and acetic acid at 40-100 °C.6 Electron-deficient dienophiles like dimethyl acetylenedicarboxylate or 1,4-naphthoquinone do not react with this triazine. 

This additional substitution of the 1,2,4-triazine nucleus with electron-donating substituents does not preclude the ability of the 1,2,4-triazine to participate in [4 + 2] cycloaddition processes with electron-rich dienophiles including ynamines.97 The [4 + 2] cycloadditions of electron-rich 1,2,4-triazines are summarized in Table 10-IX. 

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