Stannanes ipso substitution

In addition to the radical ipso-substitution of indolyl sulfones producing stannanes described earlier <96T11329>, Caddick has also reported an approach to fused [l,2-a]indoles based on the intramolecular cyclization of alkyl radicals. Thus, treatment of 112 with BuaSnH leads to the fused ring derivatives 113 (n = 1-4) <96JCS(P1)675>. 

Thienyl- and 3-thienyl-(tributyl)stannanes react with chlorosulfonyl isocyanate at 20°C to give the corresponding sulfonyl isocyanates by ipso-substitution (Scheme 78). The yields are > 90% (93JOC7022). 

Instead of DIB, iodosylbenzene underwent the same reaction, with better yields in some instances. Also, propargylgermanes and stannanes could replace the silanes. Ipso substitution products resulted in some p-methoxy-substituted DIBs on treatment with two equivalents of propargylsilanes ... 

Cine substitution is encountered occasionally as a result of a slow transmetallation step when sterically encumbered stannanes are used. Flohr [8] carried out studies designed to find a system suitable for the Stille coupling between sterically congested vinyltins and aryl iodides or trifiates he found that under certain conditions the iodides gave ipso products, while the trifiates under somewhat different conditions afforded cine substitution (Scheme 6.3). He also found that the addition of copper iodide was essential for successful coupling of aryl iodides. Mechanistic explanations of this abnormal cross-coupling mode (cine product)... 

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