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21.1.4.2.1.5 Variation 5: Ammonia Equivalents for the Palladium-Catalyzed Preparation of N-Unsubstituted Amides

DOI: 10.1055/sos-SD-021-00092

Cook, G. R.Science of Synthesis, (200521125.

The direct use of ammonia as the nitrogen source for the preparation of N-unsubstituted amides is fraught with difficulties. This is mainly due to the high temperatures required for the aminocarbonylation process, and utilizing ammonia gas is hazardous and not very practical. Thus, methods to synthesize N-unsubstituted amides have relied on protected amine sources that can be easily deprotected. For example, hydroxylamines can be utilized in palladium-catalyzed carbonylative coupling with vinyl iodides or trifluorometh­anesulfonates in high yields.[‌33‌] This then requires reduction of the resulting hydroxamide NO bond. The direct utilization of nitrogen gas with lithium and titanium(IV) isopropoxide has also been reported in carbonylation reactions.[‌34‌,‌35‌] A more convenient ammonia synthon is hexamethyldisilazane 50 (Scheme 20).[‌36‌] Palladium-catalyzed carbonylative coupling with iodobenzene, followed by acidic hydrolysis provides benzamide (51) in 76% yield. In general, aryl iodides are optimal for this process. Aryl and vinyl trifluoromethanesulfonates are less efficient and lower yields are obtained.

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