Aldehydes arylstannanes

The nucleophilic addition of organometallic reagents to imines provides an attractive route to amines [4]. Recendy, however, some completely different approaches to the synthesis of a-aryl amine were reported. Hayashi and Ishigeda-ni found a new catalytic system for the asymmetric addition of arylstannanes to imines derived from aromatic aldehydes (Scheme 11) [20]. 

Phosphorus oxide chloride Ar. aldehydes from arylstannanes Vilsmeier-type formylation... 

Rhodium catalysts have been widely used for C-C bond formation processes [71], Particularly noteworthy are the Rh(I)-catalyzed additions of boronic acids and their derivatives to a.p-unsaturated carbonyl compounds [72-78] and aldehydes [75, 79] (Chapter 4). The groups of Miyaura and Hayashi have shown that Rh(I) catalyzes the addition of sodium tetraphenylborate and arylstannanes to N-sulfonylimines [80-82]. Miyaura and co-workers have also reported the first example of a Rh(I)-cat-alyzed addition of an arylboronic acid to an N-sulfonylimine (77), to give sulfonamide 78 (Equation 13) [83]. Reactions proceeded with 2 equivalents of arylboronic acids using either a cationic Rh(I) catalyst alone, or in combination with appropriate phosphine ligands such as bis(diphenylphosphino)propane or P(i-Pr)3. Boronic esters will also react, particularly in the presence of triethylamine. The reaction does not proceed with simple aldimines, such as PhCH NPh. 

Another approach to the conversion of aryltrifluoroborate salts into aryl fluorides also used a common copper salt to promote the reactions however, this chemistry used an electrophilic source of fluorine (Scheme 7.58) [84]. The most effective source of F was found to be A-fluoro-2,4,6-trimethylpyridinium ttiflate. Similar to the authors previous work with arylstannanes, the key to the synthesis was prestirring the F source and the copper complex prior to the introduction of the aryltrifluoroborate salts. Using this system, a wide range of aryltrifluoroborate salts bearing ethers, halogens, aldehydes, ketones, amides, and esters were converted into aryl fluorides. 

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