Acylaminal formation

Through Oxidative Carbon-Carbon Bond Cleavage 184 5.2. Fragment Coupling Through N-Acylaminal Formation and ... 

SCHEME 9 Acylaminal formation through nitrile hydrozirconation, acylation, and alcohol addition. 

Fragment Coupling Through /V-Acylaminal Formation and Completion of the Synthesis... 

The N-oxides of isoquinolines have proved to be excellent intermediates for the preparation of many compounds. Trialkylboranes give 1-alkyl derivatives (147). With cyanogen bromide in ethanol, ethyl N-(l- and 4-isoquinolyl)carbamates are formed (148). A compHcated but potentially important reaction is the formation of 1-acetonyLisoquinoline and 1-cyanoisoquinoline [1198-30-7] when isoquinoline N-oxide reacts with metbacrylonitrile in the presence of hydroquinone (149). Isoquinoline N-oxide undergoes direct acylamination with /V-benzoylanilinoisoquinoline salts to form 1-/V-benzoylanilinoisoquinoline [53112-20-4] in 55% yield (150). A similar reaction of AJ-sulfinyl- -toluenesulfonamide leads to l-(tos5larriino)isoquinoline [25770-51-8] which is readily hydrolyzed to 1-aminoisoquinoline (151). 

Resin-bound diols, amino alcohols, and dithiols, which reversibly form cyclic acetals with aldehydes and ketones, have been successfully used as linkers for carbonyl compounds (Entries 5-11, Table 3.40). Acetal formation on insoluble supports can be achieved by azeotropic removal of water (C6H6, TsOH, reflux [720]), whereas dithio-acetals can be prepared by acid-catalysis alone (BF3 OEt2 or TMSC1 CHCI3,0 °C, 2 h [721]). /V-Acylaminals such as R-CFI(OMe)NFI-CO-Pol have been prepared by treatment of resin-bound amides H2NCO-Pol with aldehydes in the presence of HC(OMe)3 and TFA [722],... 

Treatment of an w-acylaminal derivative 83 with allylsilanes in the presence of a Lewis acid or a Brpnsted acid gives the corresponding condensation products (equation 55)122-125. The reaction can also proceed intramolecularly, e.g. in the formation of 84 and 85 (equations 56 and 57). A piperidine skeleton 86 can also be formed by such intramolecular cyclization (equation 58)126. 

The /V-acylaminals 136 can serve as substrates for the formation of fused azepinone derivatives on treatment with a catalytic amount of TiCh, although the reaction is sensitive to the nature of the R group. Thus, 138 was obtained from 136 (R = CH2OAc), but with R = Me in 136, the 6,6-fused system 137 resulted (Scheme 18) <1999TL7939>. 

The synthesis of alkaloids described above is based on the generation of a cationic center at the position a to the nitrogen atom of an amide followed by a carbon-carbon bond formation at the a-position as the key reaction. On the other hand, developing an anionic center at the a-position of the N-acylamine generally requires a very strong base which may bring about undesirable side reactions. However, the formation of... 

E)-acylamine (285), which in the Diels-Alder reaction must have a transition state where the W-acyl group is endo and the ester group is exo in order to account for the formation of the trans product (286) (80JA1153). 

Ring closure of acylamines prepared from ethylenediamine also yields imidazoles,88 but this reaction will be discussed in Section II, E as formation of the 1 2- and 2 3-bonds. When 2,2 -dipyridyl compounds react with methylene iodide,84 bromine in pyridine, or p-toluenesulfonyl chloride in pyridine,85 imidazolium salts are produced. 

The next part is devoted to the D-fructosylamines the substituted amino function includes acyl- as well as aryl-amines, and even amino acids. At the time of the previous review,principally acylamines had been synthesized, but the mechanism of formation has since been elucidated, and it thus became possible, by adjusting the reaction medium, to obtain higher yields and crystalline derivatives. 

Altman et al. have used the Bamberger imidazole cleavage reaction of substituted imidazoles in producing enantio-enriched vicinal di-acylamines. Specifically ring cleavage of 25 with (-)-menthyl chloroformate introduces chiral carbamate substituents on the double bond in menthyl carbamates 28 and 29. Hydrogenation of the hydrolyzed product 30 leads to preferential formation of vicinal diamide 32 over 31 in a diastereomeric ratio of 5 1. 

Trifluoroacetic anhydride Preferential formation of sec. nitramines from sec. acylamines... 

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