The rhodium(I)-catalyzed reaction of alkynes with 2-bromophenylboronic acids in the presence of paraformaldehyde resulted in a CO gas-free carbonylative cyclization, yielding indenone derivatives. [RhCl(BINAP)](2) and [RhCl(cod)](2) were responsible for the decarbonylation of formaldehyde and the subsequent carbonylation of alkynes with 2-haloboronic acids, respectively, leading to efficient whole carbonylation. Sterically bulky and electron-withdrawing groups on unsymmetrically substituted alkynes favored the alpha-position of indenones.

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Indan derivatives Q 1050Rh (I)-Catalyzed CO Gas-Free Carbonylative Cyclization Reactions of Alkynes with 2-Bromophenylboronic Acids Using Formaldehyde. -Paraformaldehyde is used as an CO source in the reaction to afford various indenones [cf. (IV)]. The ratio of the catalysts is crucial. For unsymmetrical alkynes, a sterically bulky or electron--withdrawing group favors the α-position of the carbonyl carbon in the products. The reaction of 2-bromophenyl(trimethylsilyl)acetylene (XVa) with the non-halogenated boronic acid requires the addition of styrene. The similar reaction for the phenyl or butyl derivatives fails [cf. (IVd), (XVII)]. -(MORIMOTO*, T.; YAMASAKI, K.; HIRANO, A.; TSUTSUMI, K.; KAGAWA, N.; KAKIUCHI, K.; HARADA, Y.; FUKUMOTO, Y.; CHATANI, N.; NISHIOKA, T.; Org.