Phosphoramidite basic additives

Scheme 2.137 Effect of basic additives on the hydrolysis of phosphoramidites.

As previously discussed, activation of the iridium-phosphoramidite catalyst before addition of the reagents allows less basic nitrogen nucleophiles to be used in iridium-catalyzed allylic substitution reactions [70, 88]. Arylamines, which do not react with allylic carbonates in the presence of the combination of LI and [Ir(COD)Cl]2 as catalyst, form allylic amination products in excellent yields and selectivities when catalyzed by complex la generated in sim (Scheme 15). The scope of the reactions of aromatic amines is broad. Electron-rich and electron-neutral aromatic amines react with allylic carbonates to form allylic amines in high yields and excellent regio- and enantioselectivities as do hindered orlAo-substituted aromatic amines. Electron-poor aromatic amines require higher catalyst loadings, and the products from reactions of these substrates are formed with lower yields and selectivities. 

Fig. 19 Basic steps in a cycle of nucleotide addition by the phosphoramidite method in-situ synthesis using ink-jetting. DMTr = dimethoxytrityl group...

Our current view on the mechanism of the Ir-catalyzed allylic substitution is summarized in Scheme 11.2. The complexes Cl, which are obtained by simply mixing [ Ir(diene)Cl 2] and a phosphoramidite, are catalytically inactive. Catalyst preparation involves activation with a base, which is required in order to generate the cyclometallated complexes C2 (18 valence electrons (VEs)) [3]. An additional base is not required if the nucleophile is sufficiently basic, for example, in case of benzyl or propyl amine. In our laboratory, the non-nucleophilic base TBD (l,5,7-triaz -bicyclo[4.4.0]dec-5-ene) is usually employed because it effects the... 

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