Olefins, formylation

The formyl cation, HCO, is also likely to be an intermediate in the modification of the Koch reaction whereby formic acid reacts with olefins to give carboxyhc acids (20) ... 

Oxidation. The chlorine atom [22537-15-17-initiated, gas-phase oxidation of vinyl chloride yields 74% formyl chloride [2565-30-2] and 25% CO at high oxygen [7782-44-7], O2, to CI2 ratios it is unique among the chloro olefin oxidations because CO is a major initial product and because the reaction proceeds by a nonchain path at high O2/CI2 ratios. The rate of the gas-phase reaction of chlorine atoms with vinyl chloride has been measured (39). 

The preparative value of this compound lies in the surprising fact that bis(l,3-diphenylimidazolidinylidenc-2) behaves in many reactions ie.g., with aromatic aldehydes,2,7 and with carbon acids 2 7-fJ) as if it dissociated to form a nucleophilic carbene. The hydrolytic cleavage of these derived imidazolidine derivatives makes possible the preparation of formyl compounds, so that the amino olefin can be considered as a potential carbonyla-tion reagent. In many reactions it is not necessary to isolate... 

A second convergent synthesis of haliclamine A (64) was achieved in a stepwise sequence from cyclopropyl(thiophen-2-yl)methanone (76) (Scheme 7) [37]. The protected thiophene 77 was condensed with formyl-piperidine to give 78, suitable for a Wittig olefination with 79. After desulfurization of the product 80, the deprotected alcohol 82 was subjected to homoallylic rearrangement using MesSiBr in the presence of ZnBr2. The re-... 

Although the Vilsmeier reaction is known best in aromatic systems, aliphatic olefins also undergo formylation. Synthesis of forwocortal (257) involves such a step. Formation of the monoketal of 255 involves the 3-ketone function with the familiar concomitant shift of the double bond to C-5,6. 

Immobilization of catalysts is an important process design feature (see Chapter 9.9). A recent example of catalyst immobilization is the biphasic approach which seems superior to immobilization on solids, as successfully proven in the Ruhrchemie/Rhone Poulenc process for the hydro-formylation of olefins.286 Supported liquid phase catalysis was devised as a method for the immobilization of homogeneous catalysts on solids. When the liquid phase is water, a water-soluble catalyst may be physically bound to the solid. 

Friedel-Crafts acylation reactions of aromatics are promoted by Tilv complexes.104 In some cases, a catalytic amount of the titanium compound works well (Scheme 28). In addition to acyl halides or acid anhydrides, aldehydes, ketones, and acetals can serve as electrophile equivalents for this reaction.105 The formylation of aromatic substrates in the presence of TiCl4 is known as the Rieche-Gross formylation metalated aromatics or olefins are also formylated under these conditions.106... 

An unusual series of nonterpenoid aliphatic isothiocyanates from a Fijian Pseudaxinyssa sp. was evident by their strong IR absorption [68]. After silica gel and reverse-phase HPLC experiments, the structures of (Z,Z)-1,18-diisothiocyanooctadeca-1,17-diene (134, n = 14), mp 15°C, and seven other di-olefinic a,mono-olefinic a, o>bisisothiocyanates (135, n = 9-18) and three a-isothiocyano-co-formyl mono-olefins (136, n = 9, 15, 16) were also identified by spectral data... 

Fig. 5. Associative mechanism for the rhodium-triphenylphosphine-catalyzed hydro-formylation of olefins (24-27).

Many research groups have attributed the isomerization to a series of additions and eliminations of a cobalt carbonyl hydride. However, it has been shown that aldehydes may be found with formyl groups attached to a carbon atom other than the two of the double bond even under non-isomerizing conditions. Piacenti and co-workers (44, 45) studied the hydroformylation of [l-14C]propylene and of a>-deuterated a-olefins. Even for a-olefins with chain lengths up to C6, the formyl group was attached to all possible carbon atoms in the product mixture. However, in the deuterated experiments, deuterium was present only on carbons 2, 3, and a) of the resulting aldehydes. These results were explained by pro-... 

Branching at an olefinic carbon atom inhibited the reaction markedly, the most dramatic case being that of 2,3-dimethyl-2-butene. It should be noted that the product in this case is nearly exclusively 3,4-dimethylpen-taldehyde for either cobalt or rhodium catalysis (7). Thus, a general rule that products containing a formyl group attached to a quaternary carbon atom are not formed (49) remains valid. Hydroformylation proceeds only after isomerization has occurred. 

Because of the extreme industrial importance of simple hydrocarbons such as propylene in hydroformylation, the reaction of a-olefins has been studied in much detail. As noted before, the formyl group can be attached to either of the carbon atoms which constitute the original double bond. For olefins of greater than C3 chain length, the formyl group may, under certain conditions, also be attached to a carbon atom which was originally saturated. But for propylene only two isomers are possible, as shown in Eq. (25). 

Thus, the rule of Keulemans (49), that a-quaternary carbon formyl compounds are not formed, was followed. The olefin isomerized to allow formyl attachment to a primary carbon atom. Addition of phosphine, which decreases isomerization, resulted in no reaction. 

Early studies of the cobalt hydroformylation (4) included vinyl acetate as the olefinic reactant. A mixture of a- and /3-formyl esters was reported. 

Substitution on the double-bond carbon a to the oxygen increased the difficulty of the reaction, and formyl attachment occurred exclusively on the /3-carbon [Eq. (42)]. Thus, these substituted olefins also followed the rule of Keulemans (49). 

The use of ester and formyl groups for this reaction is also possible. The reaction of methyl benzoates with olefins proceeds when the benzoates have electron-withdrawing substituents such as trifluoromethyl, cyano, and ester groups (Equation (8)).5,5a In the case of aldehydes, the reaction requires sterically hindered substituents such as tert-butyl and trimethylsilyl groups.6... 

Among the rare reports of chemical transformation of substituents attached to the ring, the total reduction of an aromatic ketone linked at C-l (lithium aluminium hydride (LAH)), then Et3SiH/trifluoroacetic acid (TFA), overall yield 20%) is of interest <1998H(48)1015>. One example related to Wittig olefination of the 1-formyl derivative of the parent heterocyle was reported to occur in low yield <2001CPB799>. 

The product of this preparation is the most enantioselective catalyst developed to date for asymmetric epoxidation of a broad range of unfunctionalized olefins.6 The procedure includes a highly efficient resolution of trans-1,2-diaminocyclohexane as well as a convenient analytical method for the determination of its enantiomeric purity. This method is general for the analysis of chiral 1,2-diamines. The Duff formylation described in Step B is a highly effective method for the preparation of 3,5-di-tert-... 

To interpret these experiments, we suggest that our data point to a stabilizing through-space interaction of a donor olefinic linkage with the formyl function as the likely source of preference of conformers II and III leading to the sense of attack anticipated by the Roush model. [7]... 

Mazet et al. have reported an efficient asymmetric isomerization reaction of allylic alcohols [60, 61]. In a preliminary report they utilized the BArp analog of Crabtree s complex to efficiently catalyze a hydride transfer from the a position of the allylic alcohol to the p position of the olefin with a concomitant formation of a formyl group. A subsequent report detailed a remarkable enantioselective variant of this process catalyzed with Ir(12g) and (12h) (Scheme 12). 

Group VA Donor Ligands. The paramagnetic compounds, [Co(CO)2(PR3)]3 (R3 = Bu5, Bu2 Ph, or Phj), have been isolated during stoicheiometric hydro-formylation reactions of linear a-olefins " viz ... 

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