Aldehydes. 738 table

Polymer-supported amino alcohols and quaternary ammonium salts catalyze the enan-tioselective addition of dialkylzinc reagents to aldehydes (Table 31). When the quaternary ammonium salt F is used in hexane, it is in the solid state, and it catalyzes the alkylation of benzaldehyde with diethylzinc in good chemical yield and moderate enantioselectivity. On the other hand, when a mixture of dimethylformamide and hexane is used as solvent, the ammonium salt is soluble and no enantioselectivity is observed21. 

Research groups at Vertex and Lilly optimized inhibitors starting from pyrazinoyl capped tetrapeptidic aldehydes (Table 2.4) [137], The main SAR... 

Hydroformylation of a range of 1,1-di- and 1,1,2-trisubstituted unsatur-ated esters yields quaternary aldehydes (Table 1, entries 1-8). Hence, the regiochemistry-directing influence of the electron-withdrawing ester function overcompensates Keuleman s rifle. Furthermore, hydroformylation of 1,2-disubstituted unsaturated esters occurred with high a-selectivity and chemoselectivity (Table 1, entries 9 and 10). As a side reaction hydrogenation of the alkene has been observed [41]. 

Silver acetylenide 239 was found to react with aldehydes (Table 8) and the ketone in Equation (133) by using a stoichiometric amount of Cp2ZrCl2 and a catalytic amount of AgOTf at room temperature to afford the corresponding 7-hydroxy-a,/3-acetylenic esters in high yields. 

This catalytic system was further studied by Strohmeier and Steigerwald, who performed reactions at 10 bar without solvent to achieve hydrogenation of a series of aldehydes (Table 15.1) [2]. Turnover numbers (TON) of up to 8000 were achieved in the case of the hydrogenation of benzaldehyde. The chemoselectivity of this catalyst towards carbonyl hydrogenation over alkene hydrogenation was... 

A novel chiral phosphonic amide-SiCl4 complex has also been found to serve as a catalyst for additions of allenyltributyltin to aldehydes (Table 9.45) [78], The reaction is limited to aromatic aldehydes because of competing formation of silylated chloro-hydrins from aliphatic aldehydes and the SiCI4 reagent. 

In a similar type of reaction, polymer-supported hydridoiron tetracarbonyl anion reacts with simple non-benzylic aliphatic bromides and iodides to produce aldehydes (Table 8.15), presumably through the intermediate formation of RCOFeH(CO)3, which undergoes reductive extrusion of the aldehydes [3], In contrast, benzylic halides and a-halocarbonyl compounds are reductively dehalogenated by the HFe(CO)4 anion (see Chapter 11). 

This trend observed for 3-formylfuran (11) (Scheme 5) could also be confirmed for other aromatic and unsaturated aldehydes (Table 5, Scheme 6). The yields that were achieved using 50 mol% together with dienolate 2 were matched with dienolate 1 using only 17 mol% of the Ti-BINOL system. Interestingly, the reaction of cinnamaldehyde with 2 gave no conversion. When aliphatic aldehydes were used, only notoriously poor yields were observed, indicating the constant problem in this type of transformation that is also encountered by other groups with different dienolates in one way or the other vide infra). 

The iridium nanoparticles showed good activity for the hydrogenation of both cyclic and acyclic saturated ketones, including an additional experiment for benz-aldehyde (Table 15.7, entry 7). The main results relating to hydrogenation reactions performed under solventless conditions are Hsted in Table 15.7. 

Utilizing prochiral a,a-disubstituted Michael acceptors, the Stetter reaction catalyzed by 76a has proven to be both enantio- and diastereoselective, allowing control of the formation of contiguous stereocenters Eq. 8 [73]. It is noteworthy that a substantial increase in diastereoselectivity is observed, from 3 1 to 15 1, when HMDS, the conjugate acid formed upon pre-catalyst deprotonation, is removed from the reaction vessel. Reproducible results and comparable enantioselectivities are observed with free carbenes for example, free carbene 95 provides 94 in 15 1 diastereoselectivity. The reaction scope is quite general and tolerates both aromatic and aliphatic aldehydes (Table 9). 

Trifluoromethylation can be achieved with the use of imidazolylidene carbene 1 [159], Song and co-workers found this transformation is tolerant of both electron-rich and electron-poor aldehydes (Table 26). Even enolizable aldehydes undergo trifluoromethylation in 81% yield (entry 3). Selective reaction occurs with an aldehyde in the presence of a ketone in the substrate (entry 5). The use of activated ketones as acceptors leads to tertiary alcohols in good yields (entries 7 and 8). 

Acetylbenzaldehyde led to the expected product with complete chemoselectivity toward the aldehyde (Table 12, entry 13). Only a moderate yield was obtained with 1-naphthyl carboxaldehyde as the substrate (Table 12, entry 14). With an... 

Generally, good yields of p-amino ester were obtained with aromatic aldehydes as well with an a,p-unsaturated aldehyde (Table 13, entries 12-16). Interestingly, we noted that the reaction was sterically sensitive because ortho substitution led to a decreased conversion (Table 13, compare entries 13 and 14). Aliphatic aldehydes... 

Our conditions were then applied to aliphatic aldehydes (Table 18). When n-butyraldehyde or cyclohexylcarboxaldehyde were reacted, the corresponding aldols 28k and 281 were obtained with moderate diastereoselectivity and poor yield due to low conversion (Table 18, entries 1 and 2). 

An alternative preparation of enantioenriched anti-homopropargylic alcohols along similar lines uses EtjZn to effect in situ transmetallation of an allenylpalladium intermediate from a propargyl mesylate and 2.5 mol % of Pd OAc)2 PPh3 in the presence of an aldehyde (Table II). The two methods are comparable. 

The potential of benzoylformate decarboxylase (BFD, E.C. 4.1.1.7) to catalyze C-C bond formation was first reported by Wilcocks at al. using crude extracts of Pseudomonas putidsL [50]. They observed the formation of (S)-2-hydroxy-l-phenylpro-panone (S)-2-HPP when benzoyl formate was decarboxylated in the presence of acetaldehyde. Advantageously, aldehydes - without a previous decarboxylation step - can be used instead of the corresponding more expensive a-keto acids [51]. We could show that BFD is able to bind a broad range of different aromatic, heteroaromatic, and even cyclic aliphatic and conjugated olefinic aldehydes to ThDP before ligation to acetaldehyde or other aldehydes (Table 2.2.7.3) [52]. 

This asymmetric a-aminoxylation can be applied to a wide range of aldehydes (Table 6.1) and six-membered cyclic ketones (Table 6.2). Because of the easy conversion of a-aminoxy moiety to the a-hydroxy group, " operational simplicity, and the... 

In their quest for alkynyl-substituted 1,2-diols, Epsztein and workers examined additions of alkoxy allenylzinc reagents to aldehydes (Table 4)5. The reagents were prepared from various propargylic ethers by lithiation with BuLi followed by addition of Znl2. Although exact ratios were not determined, the major propargylic products were surmised to be the anti isomers based on spectral data and comparison with authentic samples. 

Zweifel and Hahn found that deprotonation of terminal allenes with -BuLi and subsequent addition of ZnCb leads to terminal allenylzinc reagents, which afford anti adducts upon addition to various aldehydes (Table 5)7. Branching in the aldehyde and allene substituents enhanced the anti syn ratio of adducts, in keeping with the previously proposed cyclic transition state for such additions. 

The present procedure uses sodium methoxide in methanol for generation of the tosylhydrazone salt. This procedure gives the highest reported yield and, unlike other procedures, also gives pure diazo compounds free from solvents. This vacuum pyrolysis method appears applicable to the formation of relatively volatile aryldiazomethanes from aromatic aldehydes. Table I gives yields of diazo compounds produced by this vacuum pyrolysis method. The yields have not been optimized. The relatively volatile diazo esters, ethyl a-... 

Polymerization of aldehyde by typical cationic catalysts such as sulfuric acid and titanium tetrachloride is considered to reflect the steric factor. Acetaldehyde gave an isotactic-rich amorphous polymer whereas propionaldehyde and higher aldehydes gave isotactic crystalline ones. The yield of polymer and the stereospecificity of polymerization increased with the increase in the bulkiness of the alkyl group of the aldehyde (Table 7). 

Epoxides are reactive electrophiles, which enable the facile preparation of substituted alcohols by reaction with a broad range of nucleophiles. Epoxides can be prepared on insoluble supports either by epoxidation of alkenes or from aldehydes (Table 15.1). 

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