Hydrosilanes Are Not Always Reducing Agents for Carbonyl Compounds but Can Also Induce Dehydration: A Ruthenium‐Catalyzed Conversion of Primary Amides to Nitriles

Abstract

A practical procedure for production of nitriles is offered by the triruthenium carbonyl cluster catalyzed dehydration of primary carboxamides with hydrosilanes under neutral conditions. This is the first example that a transition-metal-catalyzed activation of Si-H bonds does not lead to the reduction

Hydrosilanes Are Not Always Reducing Agents for Carbonyl Compounds, II: Ruthenium‐Catalyzed Deprotection of tert‐Butyl Groups in Carbamates, Carbonates, Esters, and Ethers

“…[7] Strong Brønsted acids such as trifluoroacetic acid, hydrochloric acid, and sulfuric acids cleave the C-O bond of the OtBu moiety at room temperature. Lewis acids such as TiCl 4 , SnCl 4 , BX 3 , and AlX 3 (X = Cl, Br) are also effective. These have a drawback in that the reaction media is strongly acidic, and elaboration has been performed to develop the deprotection methods proceeding under neutral conditions.…”

“…As reported previously, hydrosilanes induce dehydration of primary amides to nitriles with the aid of 1. [4,5] The reaction takes place stepwise: the first step is dehydrogenative silylation towards the NH 2 moiety of primary amides to form N,O-disilyl imidates, whereas the second is elimination of siloxane from the formed N,O-disilyl imidates. In both steps, 1 behaves as a catalyst to facilitate the reaction.…”

Straightforward Uranium‐Catalyzed Dehydration of Primary Amides to Nitriles

“…This outstanding catalyst activity at low loading and mild conditions is so far unreported for other transition-metal/silane systems. [8,14] To explore the scope and limitations of the presented uranium catalyst, the dehydration of a range of primary amides was carried out ( Table 2). The reaction conditions are in agreement with Table 1, which means the corresponding amides were transformed in the presence of UO 2 -A C H T U N G T R E N N U N G (NO 3 ) 2 ·6H 2 O (2.5 mol %) and MSTFA (3.0 equiv) in DME at 100 8C for 24 h. Remarkably, the uranium-based catalyst proved to be extraordinarily active for the dehydration of 17 different substrates to give the products in quantitative yields.…”

“…In particular, the dehydration of primary amides in the presence of catalytic amounts of metal precursors (e.g., Ru, Pd, Rh, W, V, Fe) can be a proficient choice. [5][6][7][8][9][10][11][12][13][14] However, established methods based on transition-metals require harsh reaction conditions, high catalyst loadings, or the addition of silanes (SiÀH) to force the dehydration. In systems that contain metals and silanes, milder conditions are applicable, but difficulties can arise from either the production of hydrogen as a waste product and, in the presence of functional groups, the metal silane combination can act as reducing reagent and therefore reduce the scope of the protocol.…”

Copper-Catalyzed Dehydration of Primary Amides to Nitriles

“…However, the application of stoichiometric amounts of highly acidic and basic compounds disfavors the dehydration of sensitive substrate and reduces the generality of the methods. In this regard the application of transition metal catalyst turned out to be an efficient and flexible alternative and various successful procedures have been launched so far (e.g., W, Ru, Pd, Rh, V, and U) [16][17][18][19][20][21][22][23][24][25]. More recently the potential of abundant, cheap and low toxic metals (e.g., Fe, Zn) as catalysts for the dehydration of primary amides have been demonstrated [26][27][28].…”