C-Acylimine

Only a few scattered examples of Diels-Alder cycloadditions of this type of dienophile have been described to date, and not all C-acylimines appear to be reactive. The indolone shown in Eq. (7)... 

Reactions of C-Acylimines with a Chiral Nitrogen-Substituent... 

Reactions of C-acylimines derived from phenylethylamine and glyoxylate proceed highly stereoselective in the presence of trifluoroacetic acid. 

C-Acylation imidazoles in, 1, 463 ortiio-Acylation 2-alkylpyridines, 1, 436 Acylimines... 

A -(l-Phenylpropyl)amidcs 3 are enantioselectively synthesized by alkylation of acylimines 2 generated in situ from N-(amidobenzyl)benzotriazoles 1 with diethylzinc in the presence of an enantiomerically pure promoter [(— )-(l/ 2.V)-A,A-dibutylnorcphcdrine, DBNE], The best results are obtained with one equivalent of 1, one equivalent of DBNE and two or three equivalents of diethylzinc in toluene at —78 =C with slow warming to room temperature before workup11. 

Another example of the addition of terminal alkynes to C=N in water is the coupling of alkynes with in-situ-generated A-acylimines (Eq. 4.32) and A-acyliminium ions (Eq. 4.33). In 2002, Li et al. developed a coupling reaction of alkynes with A-acylimines and A-acyliminium ions mediated by Cu(I) in water to generate propargyl amide derivatives.57 Either an activated imine derivative or imininum derivative was proposed as the intermediate, respectively. 

In neutral solvent, nitrosamides LXII readily undergo photolysis to give N-acylimines as the primary products which are susceptible to nucleophilic attack due to the conjugated C=N-C0 group (44). Photolysis of nitrosamide LXIIa in methanol gives LXVII (45%) and LXVIII (23%) obviously derived from the nucleophilic addition of methanol to and proton migration of LXVI, respectively. Photolysis of LXIIa in ether gives LXVIII (27%)... 

A library of chiral zinc complexes formed in situ by the combination of achiral and racemic diimines with 3,30-di(3,5-ditrifluoromethylphenyl)-BINOL and diethylzinc have been evaluated in the asymmetric addition of diethylzinc to V-acylimines.126 High enantioselectivities of up to 97% ee and yields of up to 96% have been achieved for a wide range of aromatic imines in dichloromethane at -30 °C. 

Simple 5(4//)-oxazolones are stable at moderate temperatures. The diphenyl derivative (183) yields the acylimine (184) on flash vacuum pyrolysis (equation 23) (80AG(E)564). The presence of acyl substituents at C(4) destabilizes the ring such compounds rearrange at 180 °C to oxazoles by a process akin to that described in Section 4.18.3.1.2(i) (equation... 

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. 

Miscellaneous Reactions.—Irradiation of acetoxy-steroids in HMPA-H20 at 254 nm gives the corresponding hydrocarbons in high yields.255 Photolysis of either a 12a-azido- (326) or a 9a-azido-ll-ketone (328) gave the corresponding aza-c-homo-compound (N-acylimine) (327) or (329), respectively. Azido-ketones in rings A or D gave complex mixtures of products.256... 

Af-Trimethylsilyl enamines undergo TV-acylation on treatment with acid chlorides (replacement of the trimethylsilyl group) to give the amide and starting ketone on hydrolysis. However, in the presence of potassium fluoride and a catalytic amount of crown ether, C-acylation occurs to give the a-acylimine in high yield196 (Scheme 85). 

TV-Acylimines of hexafluoroacetone form [1-1-4] cyclotidducts with diazomethane and diethoxy-carbene, while N-acylimines of trifluoroacetaldehyde form aziridines when reacted w ith diazomethane. Other N-substituted imines of hexafluoroacetone provide pyrazolines at 0 C or aziridines at room temperature, through two competitive processes. ... 

A comprehensive kinetic study examining the reactivity of N-acylimines/N-acyliminium salts versus imines/iminium salts has not, to date, been published. Spectral data ( C NMR), however, would suggest... 

Acyiiminium ions can also be created by treatment of the easily accessible enamides (63) with protic acids (Scheme 31 see also Section 4.2.2.1). Alternatively, transformation of enamides (63) to (60) can be achieved with C-electrophiles, by simultaneous formation of carbon-carbon bonds (cf. Scheme 37). In contrast, considerably less importance can be attributed to the comparable preparation of (60) from acylimines (64 Scheme 31), by protonation for example, due to their usually pronounced instability. 

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