Alkynes formylation

In 1995, Ogawa et al. reported the Rh-catalyzed thioformylatiori of alkyne, that is, addition of RS and formyl groups onto adjacent carbons to provide 23 (Eq. 7.17) [27]. 

This reaction exemplified that the regiochemistry of RS and H introduced by car-bonylahve addition differed from that of those by simple hydrothiolation. In the Rh-catalyzed hydrothiolation, the ArS group added to the terminal carbon and H to the internal carbon (Eq. 7.12). On the other hand, in the Rh-catalyzed thioformylation, RS was placed at internal carbon and formyl at the terminal carbon in spite of using the same catalyst precursor, [RhCljPPhsjs], which was also active for the thioformylation shown in Eq. (7.17). In 1997, the Pt-catalyzed hydrothiocarboxylation using RSH, alkyne and CO was reported to furnish 24 (Eq. 7.18), which showed the same regiochemistry as the Ni-catalyzed reaction shown in Eq. (7.1) [28]. 

The reaction of 2-formyl- and 2-acetylarylpalladium(n) bromide complexes 201 with internal alkynes and TIOTf affords indenols at room temperature, whereas cationic 2-formylarylpalladium(ll) pyridine complexes 202 do not react with alkynes at room temperature but afford indenones at 90 °C (Scheme 94). 

A moderate pressure (>5 atm.) of CO in the reaction system leads to the selective formation of 29, while alkynes undergo rhodium-catalyzed hydrosilylation with a hydrosilane to afford vinylsilanes in the absence of CO. The presence of the rhodium complex is crucial for the smooth progression of siiyiformyiation, regardless of the presence of mononuclear or polynuclear complexes. This generalization is supported by the studies of many others [15]. The most important feature of this reaction is the excellent regioselectivity, which favors the formylation of the internal sp-carbon of the acetylenic bond of terminal... 

The use of terminal alkynes in the iminoannulation process follows a different mechanistic pathway. The coupling of 7V-methyl-3-formyl-2-iodoindole and phenylacetyle was carried out in a stepwise manner,... 

Ojima and co-workers have also extensively studied the catalytic silylformylation of alkynes, employing a number of rhodium and rhodium-cobalt mixed metal complexes.122 The reaction of 1-hexyne with hydrosilanes under either ambient pressure or 10 atm of CO is catalyzed by a variety of metal complexes to yield (Z)-l-silyl-2-formyl-l-hexene, 1, and/or ( )-l-silyl-l-hexene, 2 [Eq. (48)].122a>c... 

The reactions of 1-alkynes with HSiMe2Ph catalyzed by Rh2Co2(CO)i2 proceed at 25 °C and ambient pressure of CO in toluene, yielding (Z)-2-formyl-l-silyl-l-alkenes... 

Although the regioselectivity for the silylformylation of 1-alkynes is excellent, that of internal alkynes is low except for 2-alkynoates (vide supra). Also, in the reactions of 1-alkynes, the silyl group is always delivered to the terminal position and the formyl to the C-2 position, thus it is impossible to synthesize 3-silyl-2-alkenals, which requires opposite regioselectivity. Intramolecular directed reactions can circumvent these limitations and expand the scope of the silylformylation of alkynes. 

Scheme 25 [2 + 2] Cycloaddition of steroidal formyl enamides with various alkynes...

Research on intermolecular hydroacylation has also attracted considerable attention. The transition-metal-catalyzed addition of a formyl C-H bond to C-C multiple bonds gives the corresponding unsymmetrically substituted ketones. For the intermolecular hydroacylation of C-C multiple bonds, ruthenium complexes, as well as rhodium complexes, are effective [76-84]. In this section, intermolecular hydroacylation reactions of alkenes and alkynes using ruthenium catalysts are described. 

Tandem intramolecular silylformylation-allylation reaction of diallylhydrosilyl ethers derived from homoallyl alcohols is convenient for rapid, stereoselective synthesis of 1,3,5-triols convertible to more oxygen-functionalized compounds (Scheme 12).142,142a,142b 143 [ he second uncatalyzed allylation step would be facilitated by the formation of a strained silacycle intermediate, which has enough Lewis acidity to activate the formyl group. A similar tandem reaction via alkyne silylformylation has been reported.144... 

The procedure for the final elimination reaction is essentially that of Rosenblum, et al.2 A more detailed procedure is provided which improves reproducibility. Treatment of an ethereal solution of (2-formyl-1-chlorovinyl)ferrocene with sodium amide in liquid ammonia under anhydrous conditions is also an acceptable method,5 along with the method described which employs base-induced elimination using aqueous sodium hydroxide in dioxane.2 6 Compounds of the n-haloferrocene type are converted more or less quantitatively into alkynes by dehydrochlorination using... 

Reduction of CO and ketones Hydro formylation Fischer-Tropsch synthesis Synthesis of methanol from CO Hydrogenation of amides Alkyne cyclization Hydroxymethylation... 

Catalytic hydroamination of imsaturated carbon-carbon bonds has a strong potential for the access to a large variety of amines, enamines or imines [90]. The first addition of a N-H bond to alkynes catalyzed by a ruthenium catalyst was described in 1995 by Watanabe et al. [91], and involved a ruthenium-catalyzed addition of the N-H bond of N-formyl anilines to terminal alkyne (Scheme 8.29). 

The MO data for cyano-, formyl- and ethynylacetylene (Figure 6) fail to indicate the correct positional isomer. Instead of C, attack, C/a or Michael addition products are the rule for these terminal alkynes (equations 32-34). Of course, when nucleophilic attachment occurs at C j, the substituents are capable of stabilizing incipient... 

A more recent example of a functionalized alkyne addition can be seen in Crimmin s synthesis of tala-romycin A (equation 42). ° This particular alkynide is an equivalent of the formyl acetone dianion and its use has been generalized as an entry into the spiroketal portion of the milbemycins (Scheme 20). This approach differs from the Hanessian strategy in that formation of the C(17> (21) pyran ring is constructed last, through use of the alkynic unit. 

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