Imine allenyl

Gevorgyan and co-workers demonstrated that allenyl imines can be formed in situ by treating alkynylimines with a base (see Section 15.8, compound 185) [71, 72]. The same principle also works for the in situ formation of allenyl ketones from alkynyl ketones and their conversion to furans with a copper(I) catalyst [71, 72]. That Cu(I) would catalyze the isomerization of an allenyl ketone was known from work of Hashmi et al. [57, 58],... 

A related amination/rearrangement/cyclization tandem sequence had been introduced by Cossy [49]. Starting from cyclic epoxyketones 224 the reaction with propargylamines 225 caused an oxirane-opening condensation process to generate the enaminoketones 226. Upon heating in toluene to reflux, aza-Claisen rearrangement delivered the intermediate allenyl imines 227, which... 

When, instead of aldehydes, A-tosyl imine 196 is used as an electrophile in a reaction with lithiated methoxyallene 183, allenyl imines 197 result. As shown in Scheme 26, they can be converted into pyrrole derivatives 198 and 199"" . 

The proposed mechanism involves the initial rearrangement of alkynyl imine 137 into allenyl imine 138. Subsequent coordination of copper(I) to the terminal bond of the allene triggers intramolecular attack of the aromatic ring, a process that finally leads to quinolines 139 via several intermediates. 

Q -electron-donating effect of fluorine to control the regiochemistry (Scheme 3). Analogous to silicon, tin is also used to direct the Nazarov cyclization. " The interrupted Nazarov reaction has been developed by West et al. to extend the reaction of the cationic endocyclic intermediate with carbon nucleophiles. Furthermore, this reaction has been extended to imino-Nazarov cyclization of vinyl allenyl imine. ... 

Ila and Junjappa utilized a facile cycloisomerization of transient skipped allenyl imines 354 in the Cu(I)-catalyzed two-component 3 -b 2 synthesis of 2-thiopyrroles 355 (Scheme 8.123) [316]. The key intermediates 354 were accessed via the CuBr-promoted Sn2 substitution reaction ofpropargyl bromide 353 with N,S-acetals 352. A subsequent 5-mdo-dig cyclization afforded a variety of 1,2,3,5-tetrasubstituted and even 1,2-fused pyrroles in moderate to good yields. 

Step 1 To an oven-dried small vial containing a solution of a-amino allene (1.0 mmol) in anhydrous DCM (2mL) was added anhydrous MgS04 (100 mg) and aldehyde (1.0 mmol). The reaction was stirred at room temperature for approximately 5—8 h, at which point the complete conversion of starting material to imine was confirmed by crude NMR. The resulting mixtrue was filtered through celite and concentrated to obtain the skipped allenyl imine as an orange oil which was carried over to the next step without further purification. 

Step 2 To a flame-dried round-bottom flask equipped with rubber septum and N2 line was added anhydrous DMF (2mL), skipped allenyl imine (0.689 mmol), and aryl iodide (0.758 mmol). N2 was bubbled through the solution for 30 min to eliminate O2. Pd(PPh3)4 (0.069 mmol), and NaOAc (2.067 mmol) were then added. The reaction was stirred at 80° C for 12 h under N2 then exposed to air and stirred for another 12 h, maintaining a temperature of 80°C. Subsequently, the mixture was cooled to room temperature. 10 mL of H2O was added and the product was extracted with Et20 (10 mL X 3). The organic layer was concentrated to yield a crude mixture which was purified via flash column chromatography on silica gel with 0 to 10% EtOAc in hexanes gradient elution system to obtain the pyridine products. 

Accordingly, the photochemical [4+1] cycloaddition of allenyl imines and carbon monoxide leads to 3-alkylidene-4-pyrrolin-2-ones (Scheme 4-305). ... 

Ma et al. described the palladium(0)-eatalyzed three-component tandem double-addition-cyclization reaction of 2-(2,3-allenyl)malonate 218, Phi, and A-Ts-imine 219 for the stereoselective synthesis of 2,5-m-pyrrolidine 220... 

This system was described in one report and has been synthesized by a copper-assisted cycloisomerization of alkynyl imines. The authors proposed the following mechanism at first, 372 could undergo a base-induced propargyl-allenyl isomerization to form 373 next, coordination of copper to the terminal double bond of the allene (intermediate 374) would make it subjected to intramolecular nucleophilic attack to produce a zwitterion 375. The latter would isomerize into the more stable zwitterionic intermediate 376, which would be transformed to the thiazole 377 (Scheme 55) <2001JA2074>. 

Lewis acid-catalyzed ene reactions proceed between allenyl sulfides, e.g. 330, and aldehydes 329 to afford cis-trans mixtures of 1,3-butadienes 331 (Scheme 8.90) [168, 175b], Similar ene reactions observed with imines such as 332 provide the corresponding allylamines [168,177]. It was also found that the ene reaction of 1-silylated allenyl sulfide 333 with various aldehydes (or acetals) furnishes a,/l-unsaturatcd acyl compounds such as 334 and 335 under BF3-etherate catalysis [175b]. 

A tertiary homopropargylic alcohol could also be prepared by treatment of ethyl acetate with two equivalents of B-allenyl-9-BBN. However, the reaction proceeded slowly and was not general for other esters, which proved to be unreactive, as were tertiary amides and alkyl halides. However, homopropargylic amines could be prepared in high yield and with minimal allenic byproduct through allenylboration of imines with B-allenyl-9-BBN (Eq. 9.24). 

A fundamentally different approach to the synthesis of 3-pyrrolines is evidenced in the annulation in Eq. 13.50 [58]. Ethyl 2,3-butadienoate 150 reacts with N-sulfony-limine 151 in the presence of triphenylphosphine under very mild conditions to give JV-protected 3-pyrroline 152 in 90% yield. The mechanism that has been postulated is related to that of the Baylis-Hillman reaction. Michael addition of triphenylphosphine to the allenyl ester generates a zwitterion that combines with the imine to give 153 in a non-concerted process. This is followed by ring closure, proton exchange and expulsion of triphenylphosphine to give 152. This annulation is successful only for aromatic or cinnamyl imines [59]. 

Imidates, rearrangement of, 14, 1 Imines, additions of allyl, allenyl, propargyl stannanes, 64, 1 additions of cyanide, 70, 1 as dienophiles, 65, 2 synthesis, 70, 1 Iminium ions, 39, 2 65, 2 Imino Diels-Alder reactions, 65, 2 Indoles, by Nenitzescu reaction, 20, 3 by reaction with TosMIC, 57, 3 Ionic hydrogenation, 71, 1 Isocyanides, in the Passerini reaction, 65, 1... 

Diazoalkanes, like azides, are 1,3-dipoles of the propargyl-allenyl type (Scheme 87)15 and their reaction with imines provides a route for building the triazoline framework from the C—N—N and C—N fragments. Although diazomethane addition to the carbon-carbon double bond was achieved by von Pechmann in 1898,325 its reaction toward the carbon-nitrogen double bond was investigated only 50 years later. 

Scheme 3.57 Allenyl sulfides imination/sigmatropic rearrangement sequence.

Four cationic palladium intermediates in the Pd(0)-catalysed three-component cascade double addition-cyclization of organic halides, 2-(2,3-allenyl)malonates, and imines have been characterized by the high-resolution ESI-FTMS technology.84... 

Allyltriorganosilanes react with activated C-N double bonds such as iminium salts and Lewis acid-coordinated imines at the y-position to give homoallylamines.14,118 For example, in the presence of BF3, iV-acylimines generated in situ by the reaction of aldehydes or acetals with carbamates are efficiently allylated with allyltrimethylsilanes (Equation (26)).119,119a,12° The use of homochiral crotylsilanes such as 20 leads to highly diastereo- and enantioselective synthesis of homoallylamines (Equation (27)). a Allenylation of the iV-acylimines can be performed with propargylsi lanes. 

Scheme 12. Proposed mechanism for the formation of cis-pyrolidine derivatives from imine, iodobenzene and 2-(2,3-allenyl)malonate by ESI(+)-FrMS, m/z values are given for observed cationic intermediates.

Cyanothiazoles 33 are prepared from A -vinyl-l,2,3-dithiazolimines 31, obtained from the reaction of 4,5-dichloro-l,2,3-dithiazolium chloride 29 with aziridines 28 <05H(65)1601>. Thermolysis of imines 31 brings about cyclization to give sulfur, hydrogen chloride and 2-cyanothiazoles 33, possibly by an electrocyclization and fragmentation process. Reaction of allenyl isothiocyanate 34 with a variety of nucleophiles (NuH) leads to... 

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