Aldehydes using

The reduction of acyl halides with hydrogen to form aldehydes using Pd catalyst is well known as the Rosenmund reduction[756]. Some acyl chlorides give decarbonyiation products rather than aldehydes under Rosenmund conditions. The diene 890 was obtained by decarbonyiation in an attempted Rosenmund reduction of acetyloleanolic acid chloride (889)[757], Rosenmund reduction of sterically hindered acyl chlorides such as diphenyl- and tnpheny-lacetyl chloride (891) gives the decarbonylated products 892[758],... 

A more recent method (31) is to prepare the Aj-thiazoline from the mercaptoacetaldehyde dimer, ammonia, and an aldehyde using Asinger s method (32). 

Glycols are obtained by treatment with a ketone using alkali as catalyst or with an aldehyde using alkaU or copper acetyUde as catalyst (201,202). 

Regioselective coniugale reduction and reductive silylation of a,p-unsaturated ketones, esters, and aldehydes using a stable copper (I) hydride cluster (Ph3P)CuH 6... 

The products are amorphous resins whose rigidity and softening point depend on the aldehyde used. Poly(vinyl butyral), with the larger side chain, is softer than poly(vinyl formal). Since the reaction between the aldehyde and the hydroxyl groups occurs at random, some hydroxyl groups become isolated and are incapable of reaction. A poly(vinyl acetal) molecule will thus contain ... 

The carboranyl alcohol can also be prepared from the stannyl carborane and an aldehyde using Pd2(dba)3-CHCl3/dppe. The carborane is stable to Brpnsted and Lewis acids and to LiAlH.. 

A syn-selective asymmetiic nih o-aldol reaction has been reported for structurally simple aldehydes using a new catalyst generated from 6,6-bis[(tiiethylsilyl)ethynyl]BINOL (g in Scheme 3.18). The syn selectivity in the nitro-aldol reaction can be explained by steric hindrance in the bicyclic transition state as can be seen in Newman projection. In the favored h ansition state, the catalyst acts as a Lewis acid and as a Lewis base at different sites. In conbast, the nonchelation-controlled transition state affords anti product with lower ee. This stereoselective nitro-aldol reaction has been applied to simple synthesis of t/ireo-dihydrosphingosine by the reduction of the nitro-aldol product with H2 and Pd-C (Eq. 3.79). 

A similar synthesis starting with l-(2-nitrobenzyl)pyrrol-2-aldehyde used ethanol-ethyl acetate as solvent (62). Indoles are prepared in excellent yield by hydrogenation of o-nitrobenzyl ketones over Pd-on-C (i). Azaindoles are correspondingly prepared from nitropyridines (97). 

Asymmetric (fj-butcnylborations of aldehydes using chiral 1-chloro- and l-methoxy-2-butenylboronates 4 and 5 are summarized below1 12-25-33... 

An interesting and stereoselective synthesis of 1,3-diols has been developed which is based on Lewis acid promoted reactions of /f-(2-propenylsilyloxy (aldehydes. Using titanium(IV) chloride intramolecular allyl transfer takes place to give predominantly Ag/r-l,3-diols, whereas anti-1,3-diols, formed via an / / /-molecular process, are obtained using tin(IV) chloride or boron trifluoride diethyl ether complex71. 

Diallyldialkylstannanes with chiral alkyl substituents on the tin, show variable asymmetric induction in their Lewis acid catalyzed reactions with aldehydes. Using bis-(/f)-2-phenylbutyl-(di-2-propenyl)stannane, enantiomeric excesses of up to 54% were obtained via attack on the / e-face of the aldehyde96. 

The best procedure reported to date for the asymmetric allylation of aldehydes using tributyl(2-propenyl)stannane involves the catalyzed addition with the BINOL-TiCl2 complex as catalyst. Good yields and ee s were obtained for both aromatic and aliphatic aldehydes using 20 mol% of the catalyst127. 

A combination of substrate-induced and auxiliary-induced stereoselectivity is provided by the diisopinocampheylborinates 11a and lib derived from the chiral ketone (S)-l-benzyloxy-2-mcthyl-3-pentanone52. Whereas this ketone provides no significant diastereoselectivity when converted into the dibutylboron enolate and, subsequently, added to aldehydes, use of the diisopinocampheyl reagents 11a and lib leads to the jS-hydroxy ketones 12 and 13 in a stereoselective manner. The chiral information which is located in the carbon chain of the starting ketone 10 is incorporated into the products ... 

Oxa-tetrahydropyridines are interesting intermediates for the preparation of pharmaceuticals and natural product based alkaloid systems. A modified Hantzsch reaction was developed under microwave irradiation for the preparation of 2-oxa-tetrahydropyridines 173 by reaction of Meldrum s acid, a /3-ketoester and an aldehyde, using NH4OAC as the source of ammonia (Scheme 62). Yields ranged from 81 to 91% at temperatures of 100-130 °C depending on the substrate (the aldehyde) employed. All the products obtained have the same structure except for the aromatic substituent in position 4 [109]. 

Similarly, Dakka and Sasson (ref. 26) showed that benzylic alcohols could be selectively oxidized to the corresponding aromatic aldehydes using HBr/H202 as the oxidant (Fig. 23). The reaction was not successful with electron-rich aromatics which underwent competing nuclear bromination. 

In many cases, the racemization of a substrate required for DKR is difficult As an example, the production of optically pure cc-amino acids, which are used as intermediates for pharmaceuticals, cosmetics, and as chiral synfhons in organic chemistry [31], may be discussed. One of the important methods of the synthesis of amino acids is the hydrolysis of the appropriate hydantoins. Racemic 5-substituted hydantoins 15 are easily available from aldehydes using a commonly known synthetic procedure (Scheme 5.10) [32]. In the next step, they are enantioselectively hydrolyzed by d- or L-specific hydantoinase and the resulting N-carbamoyl amino acids 16 are hydrolyzed to optically pure a-amino acid 17 by other enzymes, namely, L- or D-specific carbamoylase. This process was introduced in the 1970s for the production of L-amino acids 17 [33]. For many substrates, the racemization process is too slow and in order to increase its rate enzymes called racemases are used. In processes the three enzymes, racemase, hydantoinase, and carbamoylase, can be used simultaneously this enables the production of a-amino acids without isolation of intermediates and increases the yield and productivity. Unfortunately, the commercial application of this process is limited because it is based on L-selective hydantoin-hydrolyzing enzymes [34, 35]. For production of D-amino acid the enzymes of opposite stereoselectivity are required. A recent study indicates that the inversion of enantioselectivity of hydantoinase, the key enzyme in the... 

Scheme 25 Silyl alkyne-Prins cyclization of secondary homopropargylic alcohols and aldehydes using FeXs as a promoter...

Scheme 26 Synthesis of 2-aikyl-4-halo-1 -tosyl-1,2,5,6-tetrahydropyridines from A-tosyl homopropargyl amine and aldehydes using FeX3 as promotor...

The various thermal techniques give different results. Snee (1991) determined the heat of the esterification reaction between sec-butanol and propionic aldehyde using different thermal techniques. 

Scheme 5-39 Asymmetric addition of methyl phosphinate to aldehydes using heterobimetallic BINOLcatalysts LLB = La/Li/BINOL, LPB = La/K/BINOL, ALB = AI/Li/BINOL...

The scope of this methodology was extended to the enantioselective cyclo-propylation of various aldehydes using dicyclopropylzinc in the presence of this norephedrine-derived thiophosphoramidate ligand combined with Ti(Oi-Pr)4 to achieve the corresponding cyclopropyl alkanols with enantioselectivities of up to 97% ee (Scheme 3.19). ... 

Asymmetric Allylation. One of the recent new developments on this subject is the asymmetric allylation reaction. It was found that native and trimethylated cyclodextrins (CDs) promote enantiose-lective allylation of 2-cyclohexenone and aldehydes using Zn dust and alkyl halides in 5 1 H2O-THF. Moderately optically active products with ee up to 50% were obtained.188 The results can be rationalized in terms of the formation of inclusion complexes between the substrates and the CDs and of their interaction with the surface of the metal. 

As examples of the influence of a stereogenic center in the aldehydes used on the induced diastereoselectivity, the reactions of 2-763a-d with 2-746 to give the dihy-dropyrans 2-764a-d were investigated. Moreover, the reactions show that the trans-cycloadducts are formed almost exclusively using aliphatic aldehydes (Scheme 2.168). 

The second rhodium-catalyzed route which is widely used in connection with domino processes is that of hydroformylation. This by itself is a very important industrial process for the formation of aldehydes using an alkene and carbon monoxide. Finally, rhodium catalysts have also been used in this respect. 

Scheme 6/4.38. Domino isomerization/aldol reaction of allylic alcohols and aldehydes using (COT)Fe(CO)3 as catalyst.

Scheme 4.2 Strychnine is readily accessed via isostrychnine or the Wieland-Gumlich aldehyde using chemistry discovered during structural elucidation/degradation studies...

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