Ketones cycloadditions with imines

Aznar, et al. reported a proline-catalyzed imino-Diels-Alder reactions of acyclic a,p-unsaturated ketones 96 with imines 92 for the synthesis of mc50-2,5-diaryl-4-piperidones 98, Scheme 3.35 [50], The 2-amino-1,3-butadiene was generated in situ by the reaction of a,p-unsaturated ketones 96 with L-proline, followed by Diels-Alder cycloaddition with imine 92 to provide tetrahydropyridine adduct which was then hydrolyzed to the 4-piperidone 98. 

Finally, chromium imine carbenes underwent photoreaction with imines to give azadienes (metathesis) (Eq. 36), with azobenzene to give both metathesis and cycloaddition products (Eq. 37), and with ketones to give oxazolines... 

Scheme 5.9 NHC-Ni catalysed [3-I-2] cycloaddition reaction of cyclopropyl ketones or cyclopropyl imines with enones...

This chapter deals with [2 + 2]cycloadditions of various chromophors to an olefinic double bond with formation of a four-membered ring, with reactions proceeding as well in an intermolecular as in an intramolecular pattern. Due to the variety of the starting materials available (ketones, enones, olefins, imines, thioketones, etc.. . .), due to the diversity of products obtained, and last but not least, due to the fact that cyclobutanes and oxetanes are not accessible by such a simple one-step transformation in a non-photo-chemical reaction, the [2+2]photocycloaddition has become equivalent to the (thermal) Diels-Alder reaction in importance as for ring construction in organic synthesis. 

Chen extended the scope of his iminium ion catalysed [3+2] cycloaddition with azomethine imines (see Sect. 2.1.2) to encompass cyclic a,P-unsaturated ketone substrates using primary amine 147 as the catalyst [194]. Interestingly, the presence... 

Other examples of functionalized thiocarbonyl ylides that have been generated by the desilylation method are those bearing an imino group (49) (see Scheme 5.7). These ylides readily undergo [3 + 2] cycloaddition with aromatic aldehydes to afford l,3-thioxolane-2-imines of type 24 (X = RiN). The reaction with ketones is sluggish, however, and the cycloadducts are obtained in very low yield. 

Arylideneanilines are converted into fused pyridines by heating with an alkyne and an oxidizing agent such as di-isopropyl peroxydicarbonate (DP) when the aniline is unsymmetrically substituted, a mixture of isomers may be formed [3173]. a-Halo ketones (and, less efficiently, simple aliphatic ketones [2639]) react with imines to give fused pyridines in variable yields [2715]. An imine formed by reaction of a 6-aminopyrimidinedione with DMFDMA undergoes cycloaddition with an electron-deficient alkene the first product is dehydrogenated in hot nitrobenzene [3620]. 

The methods for generating acyl ketenes (Scheme 7-V) and their subsequent in situ participation in [4 + 2] cycloadditions with a wide range of hetero- or olefinic and acetylenic dienophiles (Scheme 7-VI), including acyl ketenes,185 186,197 carbonyl compounds, 86-188 nitriles,1874,189,191 isocyanates and isothiocyanates,1864,190,191 ketenes,191 imines,1864,1874,191,192 carbo-diimides,l87c 190,191,193 ynamines,194 ketene acetals,1864,195 enol ethers,1864,191,196 and V-sulfinylamines197 have been extensively reviewed.5,9,12 Two reports have detailed the 4-n- participation of allenic ketones in [4 + 2] cycloaddition reactions [Eq. (51)].198,199... 

Base-catalysed elimination reactions of oxaziridines produce aldehydes or ketones together with unstable N-unsubstituted imines. Recently this reaction has been used as a synthesis method for a range of more stable N-unsubstituted ketimines thus (355) with Me COK in THF at room temperature gives (356) (90 )2", Perfluoro compound (357) has been found to undergo facile cycloaddition reactions with F2C CFC1 and acetone to yield (358) and (359) respectively2-. ... 

Cycloaddition reactions of methacryloyl isocyanate with arylideneamines <1996H(42)533> and with imines derived from ketones and alkylamines <1996H(43)2083> have been reported. However, the adducts formed by the cycloaddition between compounds 38 and 39 dissociate into the two original substrates (Equation 42). Compounds 37 could not be isolated and were confirmed only by NMR spectroscopy. The VT-NMR spectra show that the ratios of substrates to adducts are temperature dependent and that the lower the temperature, the lower the dissociation of the cycloadducts. 

Although 2-[(trimethylsilyl)methyl]allyl esters and halides react with imines to give pyrrolidines (Scheme 22),the cycloaddition reaction with carbonyl compounds requires much more drastic conditions. On the other hand, 2-[(trialkyIstannyl)methyl]allyl acetate can react with aldehydes to give furanyl compound, where the presence of trialkyltin acetate, as a by-product, is crucial to compel the reaction successfully (Scheme 23). In fact, in the presence of the hialkyltin acetate, even the 2-[(trimethyl silyl)methyl]allyl ester undergoes [3 + 2] cycloaddition reactions with aldehydes (Scheme 24) and ketones successfully.Similarly, InCls is also an efficient additive for the cycloaddition reaction and both aldehydes and ketones are suitable as sub-strates. ... 

Dipolar cycloaddition reactions with stable and easily prepared azomethine imines, for the synthesis of a diverse array of heterocycles, have attracted considerable attention [125]. The complex RhjldS-MPPlM) (47) catalyzes the highly diastereoselective [3-l-2-l-l]-cycloaddition reaction between a diazo ketone and azomethine imines [126]. The final products are multi-functionalized bicyclic pyrazolidinone derivatives isolated in moderate to high yields (Scheme 9.12). 

Ye applied his catalytic system to enantioselective p-lactam and p-lactone formations via Staudinger-like reactions with imines or ketones (Scheme 14.22). Furthermore, the reaction with benzoyldiazenes gave the corresponding oxadiazin-6-ones issue of a [4+2] cycloaddition reaction, instead of the reported [2+2] DMAP derivatives, as nucleophilic catalysts. The postulated formation of an azolium enolate upon reaction of the NHC with the ketene in these reactions was evidenced experimentally by the isolation and full characterization of such zwitterionic adducts in model reactions. ... 

Cyclopropyl ketones 32 and cyclopropyl imines 33 can also undergo [3+2] cycloaddition reactions with enones 34 in presence of NHC-Ni complexes to afford the corresponding cyclopentane compounds 35 (Scheme 5.9) [11]. The catalytic system is prepared in situ from the use of [Ni(COD),], SIPr HCl salt and KOBu, the reaction also required the use of Ti(O Bu) as an additive to improve yields and increase reactions rates. In most of the cases, th products 35 were obtained in good to excellent diastereoselectivities. 

In addition to undergoing cycloaddition reactions with alkenes and al-kynes, silenes readily undergo cycloaddition reactions with heteroatom multiple bonds such as C=0 and C=N, most commonly when the trapping reagent for the silene is either an aldehyde, ketone, or imine. In many... 

Scheme 58 [3+2] Cycloaddition of azomethine imines with a, 3-unsaturated ketones...

---