Acyl cyanation reactions

Inspection of Table 1 indicates that acylation, cyanation and enolate substitution represent the other classes of Pd- or Ni-catalyzed cross-coupling. The vast topic of Pd-catalyzed enolate -substitution including the Tsuji-Trost reaction and other -substitution reactions22 is not discussed in this chapter, and the readers are referred to pertinent reviews including that cited above. The other topics are very briefly discussed below. 

The iron-catalyzed [3 + 2]-cycloaddition (Huisgen reaction) of nitriles and carbonyl compounds as reported by Itoh et al. is one of the rare examples reported where an iron reagent can be utilized for the synthesis of 1,2,4-oxadiazoles (Scheme 9.35) [93]. In this reaction, methyl ketones are nitrated at the a-position by Fe(N03)3 to generate an a-nitro ketone. This intermediate rearranges to an acyl cyanate, which reacts further with the nitrile to give the heterocyclic product 48 in good to excellent yields (R1 = Ph, R2 = CH3 95% yield). 

Specialty Isocyanates. Acyl isocyanates, extensively used in synthetic appHcations, caimot be direcdy synthesized from amides and phosgene. Reactions of acid haUdes with cyanates have been suggested. However, the dominant commercial process utilizes the reaction of carboxamides with oxalyl chloride [79-37-8]. CycHc intermediates have been observed in these reactions which generally give a high yield of the desired products (86). 

Arylthallium bis(trifluoroacetate)s (10.70) are versatile synthons for various reactions, e.g., acylations (Larock and Fellows, 1982) and photolytic cyanations (Taylor et al., 1970), as shown in Scheme 10-93. Copper-catalyzed cyanations (Uemura et al., 1972) can be carried out at 115 °C with arylthallium (acetate)(perchlorate) (Scheme 10-94). 

When the reagent is the thiocyanate ion, S-alkylation is an important side reaction (10-43), but the cyanate ion practically always gives exclusive N-alkylation. ° Primary alkyl halides have been converted to isocyanates by treatment with sodium nitrocyanamide (NaNCNN02) and m-chloroperoxybenzoic acid, followed by heating of the initially produced RN(N02)CN. ° When alkyl halides are treated with NCO in the presence of ethanol, carbamates can be prepared directly (see 16-7). ° Acyl halides give the corresponding acyl isocyanates and isothiocyanates. For the formation of isocyanides, see 10-111. 

Acylation with potassium cyanate, phenylisocyanate and similar reagents gives ureides <8lHC(37)l. p. 102). According to experimental conditions, cyanogen affords the carboxamide (87). The anomalous reaction with o-anisylisocyanate results in the isourea (88). 

Alder, cyanation, allylation, Michael reaction, and Friedel-Crafts acylation). The same catalyst was also effective in three-component reactions such as Mannich-type reactions, Strecker, and quinoline-forming reactions. The polymer catalyst was recovered and reused many times without loss of activity (Eq. 31). 

---