Aldehydes reactions, with

Examples of the Knoevenagel reaction with aldehydes are given under crotonic acid (111,145), P-n-hexylacrylic acid (111,144), sorbic acid (111,145) and furylacryUc acid (V,10). 

Ene reaction with aldehydes is catalyzed by Lewis Acids (Et2AlCl)... 

Cycloaddition of COj with the dimethyl-substituted methylenecyclopropane 75 proceeds smoothly above 100 °C under pressure, yielding the five-membered ring lactone 76. The regiocheraistry of this reaction is different from that of above-mentioned diphenyl-substituted methylenecyclopropanes 66 and 67[61], This allylic lactone 76 is another source of trimethylenemethane when it is treated with Pd(0) catalyst coordinated by dppe in refluxing toluene to generate 77, and its reaction with aldehydes or ketones affords the 3-methylenetetrahy-drofuran derivative 78 as expected for this intermediate. Also, the lactone 76 reacts with a, /3-unsaturated carbonyl compounds. The reaction of coumarin (79) with 76 to give the chroman-2-one derivative 80 is an example[62]. 

Adducts from various quaternary salts have been isolated, in reactions with aldehydes, a-ketoaldehydes, dialkylacylphosphonates and dialkyl-phosphonates, isocyanates, isothiocyanates, and so forth (Scheme 15) (36). The ylid (11) resulting from removal of a Cj proton from 3.4-dimethyl-S-p-hydroxyethylthiazolium iodide by NEtj in DMF gives with phenylisothiocyanate the stable dipolar adduct (12) that has been identified by its NMR spectrum and reactional product, such as acid addition and thiazolidine obtention via NaBH4 reduction (Scheme 16) (35). It must be mentioned that the adduct issued from di-p-tolylcarbodiimide is separated in its halohydrogenated form. An alkaline treatment occasions an easy ring expansion into a 1,4-thiazine derivative (Scheme 17) (35). 

Organohthium and organomagnesium compounds find their chief use m the prepa ration of alcohols by reaction with aldehydes and ketones Before discussing these reac tions let us first examine the reactions of these organometallic compounds with proton donors... 

Reaction with aldehydes Gngnard reagents react with aldehydes... 

These compounds are sources of the nucleophilic anion RC=C and their reaction with primary alkyl halides provides an effective synthesis of alkynes (Section 9 6) The nucleophilicity of acetylide anions is also evident m their reactions with aldehydes and ketones which are entirely analogous to those of Grignard and organolithium reagents... 

Reactions with Aldehydes and Ketones. The base-catalyzed self-addition of acetaldehyde leads to formation of the dimer, acetaldol [107-89-1/, which can be hydrogenated to form 1,3-butanediol [107-88-0] or dehydrated to form crotonaldehyde [4170-30-3]. Crotonaldehyde can also be made directiy by the vapor-phase condensation of acetaldehyde over a catalyst (53). 

The primary and secondary alcohol functionahties have different reactivities, as exemplified by the slower reaction rate for secondary hydroxyls in the formation of esters from acids and alcohols (8). 1,2-Propylene glycol undergoes most of the typical alcohol reactions, such as reaction with a free acid, acyl hahde, or acid anhydride to form an ester reaction with alkaU metal hydroxide to form metal salts and reaction with aldehydes or ketones to form acetals and ketals (9,10). The most important commercial appHcation of propylene glycol is in the manufacture of polyesters by reaction with a dibasic or polybasic acid. 

Reactions at G-5. The C-5 atom of hydantoins can be considered as an active methylene group, and therefore is a suitable position for base-cataly2ed condensation reactions with aldehydes (44). 2-Thiohydantoins give the reaction more readily than their oxygen counterparts ... 

Reaction with Aldehydes and Ketones. Formaldehyde combines with primary and secondary alkanolamines in the presence of alkali to give methylol derivatives. For the reaction of monoethanolamine with formaldehyde (12), the reaction scheme shown in Figure 1 occurs. 

Reactions with Aldehydes and Ketones. An important use for alkylphenols is ia phenol—formaldehyde resias. These resias are classified as resoles or aovolaks (see Phenolic resins). Resoles are produced whea oae or more moles of formaldehyde react with oae mole of pheaol uader basic catalysis. These resias are thermosets. Novolaks are thermoplastic resias formed whea an excess of phenol reacts with formaldehyde under acidic conditions. The acid protonates formaldehyde to generate the alkylating electrophile (17). 

Poly(vinyl alcohol) participates in chemical reactions in a manner similar to other secondary polyhydric alcohols (82—84). Of greatest commercial importance are reactions with aldehydes to form acetals, such as poly(vinyl butyral) and poly(vinyl formal). 

Other modifications of the polyamines include limited addition of alkylene oxide to yield the corresponding hydroxyalkyl derivatives (225) and cyanoethylation of DETA or TETA, usuaHy by reaction with acrylonitrile [107-13-1/, to give derivatives providing longer pot Hfe and better wetting of glass (226). Also included are ketimines, made by the reaction of EDA with acetone for example. These derivatives can also be hydrogenated, as in the case of the equimolar adducts of DETA and methyl isobutyl ketone [108-10-1] or methyl isoamyl ketone [110-12-3] (221 or used as is to provide moisture cure performance. Mannich bases prepared from a phenol, formaldehyde and a polyamine are also used, such as the hardener prepared from cresol, DETA, and formaldehyde (228). Other modifications of polyamines for use as epoxy hardeners include reaction with aldehydes (229), epoxidized fatty nitriles (230), aromatic monoisocyanates (231), or propylene sulfide [1072-43-1] (232). 

Reactions with aldehydes and ketones. 4.11 Oxidation Attack at Sulfur... 

Pyrrolo[2,3-6]pyridine, 2-methyl-Reimer-Tiemann reaction, 4, 508 Pyrrolo[2,3-6]pyridine, 4-methyl-hydrogen exchange, 4, 502 reaction with aldehydes, 4, 503 reaction with benzaldehyde, 4, 511... 

A cyclic malonste derivative (acidic methylene) used in place of malonate in alkylations or reactions with aldehydes... 

Mixtures of anhydrous hydrogen fluoride and tetrahydrofuran are successfully used as fluorinating agents to convert 1,1,2-trifluoro-l-allcen-3-ols, easily prepared from bromotrifluoroethene via lithiation followed by the reaction with aldehydes or ketones, to 1,1,1,2-tetrafluoro-2-alkenes The yields are optimal with a 5 1 ratio of hydrogen fluoride to tetrahydrofuran The fluorination reaction involves a fluonde lon-induced rearrangement (Sf,j2 mechanism) of allylic alcohols [65] (equation 40)... 

Fluoroalkylphosphonates may also be deprotonated for use in olefination reactions with aldehydes [77] (equation 64)... 

It is possible to use the enhanced electrophilicity in condensation reactions with aldehydes in the presence of amines to form imidazoles [77] (equation 16). 

When acetic anhydride is used in the CF3CCI3 and zinc reaction with aldehydes, the initial addition product undergoes an elimination reaction to give 2-chloro-l,l,l-trifluoro-2-alkenes exclusively [60, 63] (equation 51)... 

All that has been said in this section applies with equal force to the use of organo-lithium reagents in the synthesis of alcohols. Grignard reagents are one source of nucleophilic carbon organolithium reagents are another. Both have substantial carbanionic char acter in their- car bon-metal bonds and undergo the same kind of reaction with aldehydes and ketones. 

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