Silver catalysis cyclization

Intramolecular radical cyclization of an aryl bromide and an alkyne can be used to produce dihydroquinolines (Equation 57) <1998TL2965>. An analogous reaction setup utilizes a Lewis acid-catalyzed novel one-pot domino pathway using silver catalysis in high regioselectivity (Scheme 26) <2005OL2675>. Three mole equivalents of the alkyne are used with the final cyclization step arising from alkynic addition. 

Dake s group84 published an interesting report in which AgOTf and cationic gold (I) complexes were compared for their use in the synthesis of the pyrrole scaffold. From (3-alkynyl ketones 66 (Scheme 5.29) and various primary amines 67, the imine intermediates JJ were formed in situ and the intramolecular cyclization produced various pyrroles 68. Both catalysts AgOTf (5 mol%) or Au(PPh3)OTf (5 mol%) were efficient, but the reaction proceeded more rapidly with silver catalysis. 

Few examples of ene-yne cycloisomerization reactions are seen in the literature. The first results for ene-yne cycloisomerizations were with systems bearing an heteroatom (amine or oxygen) next to the alkene counterpart (forming an enamine or an enol ether). Indeed, Dake s group reported the cyclization of enesulfonamides on alkynes (69-70, Scheme 5.30) under catalysis by platinum and silver salts.85 Catalysis using AgOTf (1 1 mol%) was particularly efficient with systems such as 69 (Scheme 5.30)... 

For primary and secondary bromides base-catalysis is required, while for tertiary bromides silver acetate or silver oxide are more effective cyclization catalysts. For tertiary substrates dehydrobromination leading to allylic hydroperoxides is a serious side reaction when base-catalysis is employed and, thus, silver ion catalysis is essential. Furthermore, the silver salts must be freshly prepared because metallic silver that might be present due to exposure to light causes decomposition of the dioxetane. The tetramethyl-l,2-dioxetane (7) was the first example prepared in this way (Eq. 13). For primary substrates, abstraction of the base-sensitive dioxetanyl hydrogens are probably responsible for the low yields. For secondary substrates, both side reactions might operate. 

Addition and cyclization reactions. Chiral propargylic amines are obtained from aUcynylation of imines by catalysis of the silver salt of IB. The enantiomer of phosphate ID also finds use in the addition of indole to a-acetaminostyrenes. One more catalyst for intramolecular hydroamination to form pyrrolidine derivatives is the silylated 3. The... 

The cycloisomerization of a-allenyl ketones to the corresponding substituted furans was the first example of a gold-catalyzed addition of an oxygen nucleophile to an allene (Scheme 4-86). Traditionally, silver or palladium catalysts were employed for cyclizations of this type advantages of gold catalysis incluiie shorter reaction times, milder conditions, an or lower catalyst loadings. Variable amounts of... 

Dihydroquinolines are obtained via Cu- or Ag-cata-lyzed A -coupling/cyclization when using 2-alkynylbenz-aldehydes, amines, and ketones, which combines metal and enamine catalysis, as demonstrated by Wu et al. [119]. 2-Alkynylbenzaldehyde derivatives have also been used as the additional nucleophile carrier in the silver-catalyzed synthesis of naphthyridines and thienopyridines recently reported by Verma et al. [120], A variety of naphthyridines and thienopyridines were prepared via dual activation using L-proline as the organocatalyst, whereas for other... 

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