Synthesis of Intermediates by Rhodium‐Catalyzed Hydroformylation

Abstract

Intramolecular additions of carbocations to a C-C triple bond or to a chlorovinyl group provide a pathway to cycloalkanones and cycloalkyl ketones. Such syntheses proceeding via ring closure which have already been redo not generally require a strongly acidic medium but can instead be performed in formic acid or trifluoroethanol. ConclusionThe methods considered in this review for the synthesis of carboxylic acids, aldehydes, and ketones are not only of preparative importance but also permit a further insight into the chemical behavior of carbocations. Thus the first generation of a "primary" vinyl cation [(55a)] devoid of stabilizing substituents was accomplished by addition of the I-adamantyl cation to acetylene and the reaction of this cation monitored. On the other hand, it has been found that the reactions of amidomethyl cations with chloroolefins in sulfuric acid do not involve a carbocation but an oxazonium ion as intermediate. These results could prove valuable for the planning of new syntheses. The availability of the starting materials should also encourage the exploitation of these reactions. (1971). (1978). Synthesis of Intermediates by Rhodium-Catalyzed Hydroformylation By Hardo Siegel and Walter Himmele[']Dedicated to Professor Matthias Seefelder on the occasion of his 60th birthdayThe reaction of olefins with carbon monoxide and hydrogen to give aldehydes is referred to as hydroformylation (0x0 reaction). As catalyst for this reaction rhodium is about three to four orders of magnitude more active than the more commonly employed cobalt. With special rhodium compounds, e. g. di-p-chlorobis(q-l,5-cyclooctadiene)dirhodium [RhCl(CsH1z)]z, in the presence of chiral phosphanes, even asymmetric hydroformylations can be achieved; however, the enantiomeric purity of the products (20-30%) is not high enough for industrial-scale syntheses.

New Aldehydes by Catalytic Diene Cycloisomerisations

“…As expected, the main differences in 1 H and 13 C NMR chemical shifts observed between the two isomeric aldehydes 1d and 1e was found in the sec-butanal fragment, in particular in the signals for the methyl group at C-7 and the α-carbonyl methylene group of C-8. Smaller differences were also observed in the rest of the carbon signals, as well for some of the signals in the 1 H NMR spectra, although the two mentioned 13 C NMR signals of the sec-butanal moiety were the most conclusive for the assignment of the stereochemistry of the aldehydes obtained from the rest of the substrates (see below). NOESY spectra show that in both isomers there is restricted rotation about the C 3 -C 7 (sp 2 ) bond (see Figure 3 for 1d), probably due to steric interactions between the gem-dimethyl system at C-4 and the sec-butanal substituent at C 3 .…”

“…[12] The hydroformylation of substrates containing substituted or endocyclic double bonds is troublesome and usually requires harsh reaction conditions. [13] A remarkable exception to this, however, is represented by reactions performed in the presence of rhodium(I) catalysts modified with bulky phosphites, such as tris(o-tert-butylphenyl) phosphite [P(O-o-tBuC 6 H 4 ) 3 ]. [14] The large cone angle of this phosphite prevents the coordination of a second phosphite to the metal centre, even when a large excess of ligand is used.…”

Rhodium catalyzed hydroformylation of kaurane derivatives: A route to new diterpenes with potential bioactivity

“…The hydroformylation of such kind of substrates usually requires harsh reaction conditions for most of the catalysts [4]. Remarkable exceptions are rhodium(I) catalysts containing bulky phosphites, such as tris(o-tbutylphenyl)phosphite, P(O-o-t BuC 6 H 4 ) 3 [5].…”

Rhodium catalyzed hydroformylation of monoterpenes containing a sterically encumbered trisubstituted endocyclic double bond under mild conditions

“…All these substrates contain exocyclic terminal double bonds, which can be relatively easily hydroformylated. On the other hand, endocyclic monoterpenes, that is, 2-carene (1), 3-carene (2), and a-pinene (3), are much more reluctant to undergo hydroformylation, and it is not surprising that the available information about their hydroformylation is scarce [11][12][13][14][15][16]. However, these reactions are very attractive because they could lead directly to aldehydes 4-6, useful as fragrances (Scheme 1) [1].…”

“…Indeed, the rhodium catalyzed hydroformylation of 2 and 3 has been efficiently achieved only under pressures as high as 600 atm at 110-120 8C [11,12]. The hydroformylation of 3 was also carried out under milder conditions (100 atm, 85 8C) employing a thiolato-bridged dimeric rhodium complex [Rh 2 (m-St bu) 2 (CO) 2 (P(OPh) 3 ) 2 ], however, moderate turnover frequencies and yields were obtained [13,16].…”