Imines with alkynes

Reactions of azomethine imines with alkynes catalyzed by copper yielding fused nitrogen heterocycles have also been reported [131]. 

The 1,3-dipolar cycloaddition of azomethine imines with alkynes could also be well facilitated by an Al203-supported copper hydroxide [Cu(0H) /Al203] (Scheme 4.21). Generally, the desired pyrazolidinones were obtained in good to excellent yields (Yoshimura et al., 2011). 

Xie H, Zhu J, Chen Z, Li S, Wu Y (2010) Synthesis of 2-trifluoromethyl quinoline by the reaction of fluorinated imine with alkyne cattdyzed by indium(III) triflate. Synlett 2010(17) 2659-2663... 

Scheme 1.12 Zirconocene-mediated cyclization of imine with alkyne, isocyanate, or aldehyde and reaction chemistry of zirconaaziridines...

Scheme 20 Ru(II)-catalysed annulation of imines with alkynes...

Jamison s enantioselective coupling of imines with alkynes and organoboranes [11]... 

In a manner analogous to classic nitrile iinines, the additions of trifluoro-methylacetonitrile phenylimine occur regiospecifically with activated terminal alkenes but less selectively with alkynes [39], The nitnle imine reacts with both dimethyl fumarate and dimethyl maleate m moderate yields to give exclusively the trans product, presumably via epimenzation of the labile H at position 4 [40] (equation 42) The nitrile imine exhibits exo selectivities in its reactions with norbornene and norbornadiene, which are similar to those seen for the nitrile oxide [37], and even greater reactivity with enolates than that of the nitnle oxide [38, 41], Reactions of trifluoroacetomtrile phenyl imine with isocyanates, isothiocyanates, and carbodiimides are also reported [42]... 

Table 26 Photo-driven reactions of Group 6 imine carbenes with alkynes ...

Based on the experimental results above and together with Wang s previous work a tentative mechanism was proposed (Scheme 20) [33]. Thus, intermediate A is formed initially through coordination of imine and alkyne to the Lewis acid. This coordination sets the stage for an addition of the alkyne to the imine leading to the propargylamine intermediate B, which then undergoes an intramolecular... 

However, with 1-hexyne or phenylacetylene, the thorium catalyst induces a dramatic inversion in regioselectivity giving imines with various amounts of dimerized alkyne (e.g., Eq. 4.84) [301],... 

Domino reactions of imines with difluorocarbene in the presence of electron-deficient alkynes lead to 2-fluoropyrroles. For instance, reaction of A-benzylideneaniline (18) with difluorocarbene yields an intermediate azomethine ylide 19 capable of undergoing 1,3-... 

The alternative building scheme C2 + Q was used by Petasis and Hu [89], who reacted various aldehydes and ketones with alkenyltitanocene derivatives 172 to obtain the corresponding allenes 173 in high chemical yields (Scheme 2.54). The reaction probably proceeds via titanocene vinylidene complexes, which can also be trapped with alkynes and isocyanides to afford allenylketene imines [90],... 

The reaction of buta-2,3-dienoates (44) with electron-deficient imines (45) in the presence of triphenylphosphene yields 3 - - 2-cycloadducts (46) in excellent yields and high chemoselectivity (Scheme 16)." The l,3-diaza-2-azoniaallene salts (47) react with alkynes, iV,iV -dialkylcarbodiimides, and Al,Al-dialkylcyanamides to produce... 

Recently, Nakamura and coworkers described a related reaction of the zinc enolates derived from /3-aminocrotonamides of type 395256. In the presence of a stoichiometric amount of Et2Zn, the latter underwent smooth addition to terminal alkynes upon heating in hexane and afforded the corresponding tetrasubstituted 2-alkylidene acetoacetamides 396 (after acidic hydrolysis of the imine) with high (Z)-stereoselectivity (equation 173). 

Trofimov s pyrrole synthesis reacts ketoximes with alkynes under strongly basic conditions (Scheme 53) (90AHC178, 94H(37)1193). A key sigmatropic rearrangement of an O-vinyloxime is followed by a typical imine-carbonyl condensation. Frequently an IV-vinylpyrrole formed from the initial pyrrole is a major by-product (92CHE510). 

Regiospecific addition took place affording good yields of thietanes 143503 and, with alkynes, diene systems were formed504. Fischer has also described the reactions of thioketones with (CO)sW=NPh which undergo metathesis with these substrates to yield N-phenyl imines 144505 as shown in equation 154. 

Several of the reactions described in Section 6.16.2.4.6.1 are two-step reactions. After the initial [2+1] addition of the silylene to the multiple bond, a second insertion reaction of a silylene into a reactive Si-X bond of the cyclopropane derivative takes place yielding four-membered ring compounds. Examples are the reactions with alkynes, nitriles, imines, and ketones. 

With alkynic 1,3-dipolarophiles the dibenzo derivatives (103) react as azomethine imines giving the adducts (104). Regiospecific addition is observed when monosubstituted alkynes are used. In some reactions the cycloadduct (104) is accompanied by a Michael adduct (e.g. 103 R2 = C(C02Me)=CHC02Me). Reaction of compound (103 R1 = Me, R2 = H) with two equivalents of DMAD gives a product which appears to be the 2 1 cycloadduct (105 R1 = Me) (73TL597, 74H(2)27). 

Finally, though not strictly a hydroamination reaction, the asymmetric addition of alkynes to imines with a copper-bis(oxazoline) complex is worth briefly mentioning.[144] The nature of the ionic liquid cation has a strong effect on the enantioselectivity of the reaction and it appears that a good balance between hydrophobicity and acidity play an important role with best results obtained with [C4Ciim][Tf2N]. 

Later, Arcadi showed that /J-keto-imines react with alkynes intramolecularly to give pyrroles. The intermolecular animation with aniliaes was later developed by Hayashi and Tanaka using a cationic Au(I) catalyst to form imines (equation 27). More recently, Arcadi etal. developed an intramolecular version for the cyclization of o-alkynylanilines to form indoles (equation 28) and Li reported a double intra- and intermolecular hydroamination to obtain A-vinylindoles. " O-Substituted hydroxylamines can also undergo this type of transformation to dihydroisoxazole derivatives. " " Tandem sequences that involve a first alkyne-hydroamination step with anilines have been recently developed " " and are similar to the previonsly discnssed additions with phenols that access isoflavone skeletons. 

Imines react with alkynes to give pyrroles (equation 29). " A related transformation of azides has been reported by the group of Toste to afford pyrroles by an acetylenic Schmidt reaction (equation 30). " In an intermolecular-related addition, gold triazolates are obtained. The intramolecnlar hydroamination of trichloroacetimidates derived from propar-gyl and homopropargyl alcohols also proceeds with cationic An(I) as catalysts. ... 

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