Friedel-Crafts acetylation of diarylacetylenedicobalt hexacarbonyl proceeds readily and in high yield. Introduction of the first acetyl substituent is a very rapid process, but the second acetyl group is introduced more slowly. In all cases, para substitution was observed, presumably because of steric factors. Deactivation of aluminum chloride by its coordination at the newly formed ketone function caused some difficulties in some cases. Competition experiments showed diphenylacetylenedicobait hexacarbonyl to be somewhat less reactive toward CH3COCI-AICI3 than anisóle. The Co2(CO)6 unit serves as a protecting group for the C^C function; diarylacetylenes cannot be acetylated directly, but their Co2(CO)6 complexes can. Oxidation of the acetylated complex with ceric ammonium nitrate releases the acetylated acetylene in good yield.
the facile addition of the alkyl halide gases where formation of ion intermediates can be excluded.A one-step addition would require retention of configuration at the carbon atom. This has been confirmed by the addition and subsequent cleavage of optically active CHsCHBrCOOCiHg. The regenerated bromoester has the same sign of rotation as the original.Thus two inversions or two retentions must be involved. Cleavage of alkyl-metal bonds with Br2 is known to almost entirely occur with retention.8 Thus the oxidative addition must also go with retention. In this case, however, because of the complexity of the ir spectrum, we were not able to decide if the addition was cis or trans.A one-step addition of silicon hydrides to d8 complexes has also been postulated.9 In agreement with our work, Sommer has shown10 that addition of silicon hydrides to Ir(CO)Cl[P(C6H6)3]2 occurs with retention of configuration at silicon.Orbital symmetry considerations do not exclude a two-step mechanism for the reaction of d8 complexes with alkyl halides (Figure lc). A possible example, which goes with inversion of configuration at carbon, has been reported.11Acknowledgment. The authors wish to acknowledge the valuable help of R. W. Johnson. Financial support came from the Atomic Energy Commission, Grant No. AT(11-1)-1087, and from a predoctoral NIH fellowship for W.
The synthetic utility of isopropenylmethyldiphenylphosphonium iodide (2), isopropenyltriphenylphosphonium bromide (3), and l-phenylvinyltriphenylphosphonium bromide (4) is compared with that of the unsubstituted vinyltriphenylphosphonium salt, 1, with respect to the preparation of heterocyclic and chain-extended species. An inner phosphonium zwitterion (10) can also be isolated from 2. Under fusion conditions, 2methyl-2H-1-benzopyran ( 13) is also formed from salts 2 and 3 with no inner zwitterion isolated in either case. A mechanism is proposed for the latter reaction.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.