N-Acylimines

Pyridine-2,3,6-trione, 4-chloro-5-methylamino-monohydrate structure, 2, 114 Pyridinium N-acylimines thermolysis, 2, 345... 

A (tert-butyldimethylsilyl)allene reacted with aldehydes and N-acylimine in the presence of TiCl4 to afford the five-membered heterocycles [190],... 

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%)... 

Subsequently it was shown that N-acylimines with their increased electrophilicity cycloadd to simple olefins,150-184 as predicted.4... 

N-Acylimines which may react as l-oxa-3-aza-l,3-butadienes represent a class of heterodienes which exhibit a close relationship to l-thia-3-aza-l,3-butadienes [13]. A very impressive application of such an l-oxa-3-aza-l,3-butadiene has been worked out by Swindell et al.[445]. The asymmetric hetero Diels-Alder reaction described therein opens a very elegant approach to the A-ring side chain of taxol. This synthesis takes advantage of the bulky chiral auxiliary attached to the dienophile 6-5 which upon cycloaddition with the l-oxa-3-aza-1,3-butadiene 6-4 yielded the 1,3-oxazine derivative 6-6. Subsequent hydrolysis, hydrogenolysis and transesterification gave the methyl ester of the taxol A-ring side chain 6-7 in good endo and excellent zr-facial selectivity (Fig. 6-2). 

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... 

Cyclic derivatives having the A -acylenamines or N-acylimines structure can be prepared starting from the cyano esters as well as from the enol forms of / -ketonitriles. 

The structures of the 2-oxazolinium, 1,3,5-oxadiazinium and 3-azapyrylium salts obtained by means of electrophilic catalysis by acylium ions102,113 point to the fact that their formation proceeds not via Af,7V-bis-acyliminium ions 332 and 333, but via the TV-acyliminium ions 322 (i.e. those protonated at the nitrogen atom). In our opinion142, the acetoxy azaallenium ions 335 can be transformed to the Af-acyliminium cations 337 by a deacylation to the N-acylimines 336, followed by protonation of the latter (equation 91). Such a process is quite possible under the conditions used for... 

The TMS-exomethylene hnker 1.50 (110), obtained from carboxyethyl PS resin and a suitable TMS alcohol, was reacted with an N-acylimine as in the imino-Sakurai protocol and then the SP transformations were performed the intermediates were cyclatively cleaved with Pd(acac)2 and dppe in refluxing THF to give highly function-ahzed pyrrohdines. 

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. ... 

Sulfoxides can act as an S—O two-atom fragment in [4 + 2] condensations. Thus reaction of DMSO with benzoyl isocyanate in the presence of boron trifluoride etherate (75IZV1206) gives the 1,3,2,5-dioxathiazine (248). Boron trifluoride induced condensation of DMSO with N-benzoyl-S,S-bis(trifluoromethyl)sulfimide (249) gives the 1,3,2,4,5-dioxadithiazine (117) (78JA985), and the N-acylimine (250) also gives a 1,3,2,5-dioxathiazine (251) on reaction with DMSO (80ZOR463). 

N-Acylimines as heterodienes in synthesis of 1,3-oxazines 89CRV1525. CycIohepta[b]-l, 4-benzoxazine, chemistry of 90H(30)1263. 

Diethylzinc also adds to N-(amidobenzyl)benzotriazoles (masked N-acylimines) in the presence of DBNE to afford an optically active amide with 76% ee (eq 26). ... 

Firestone and Christensen [207] obtained 6a-hydroxypenicillin (107a) and its derivatives through an N-acylimine intermediate (106), but these had a markedly lower activity compared to the 6a-methoxy derivative (100). There is a direct one-step route to 6a-methoxypenicillin sulphox-ides (108) [208], which were converted into cephalosporins via a subse-... 

As a final test of the synthetic strategy in the indolizidine alkaloid field, Weinreb turned to the fungal neurotoxin slaflamine (132) (82JA7065). Methylol acetate 125 was prepared in several steps from amide 124. When methylol acetate 125 was heated in refluxing o-dichlorobenzene, a separable 1 1.8 mixture of epimeric Diels-Alder adducts 127 and 128 (82%) was obtained via the N-acylimine intermediate 126. Catalytic hydrogenation of adduct 127, followed by basic hydrolysis, produced acid lactam 129. Curtius rearrangement of this compound led to carbamate lactam 131 (70JA7615) and to racemic slaflamine (132) (Scheme 18). 

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... 

The a-amidoalkylation reaction, which involves the addition of carbon nucleophiles (primarily aromatic rings, alkenes, cyanides, isocyanides, alkynes, organometallic and active methylene-containing compounds) to substituted amides (89) where X is a leaving group (Scheme 17), has been extensively re-viewed. A variety of organometallic condensations have since been reported which extend the scope of this reaction. The reactive intermediates in these reactions are considered to be N-acylimines (88) or N-acyliminium salts (SKI). Direct displacement of the a-haloalkylamide precursors (89 X = halogen) cannot in certain cases be discounted. 

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