Aromatic aldehydes, olefination

Aliphatic Aldehyde Syntheses. Friedel-Crafts-type aUphatic aldehyde syntheses are considerably rarer than those of aromatic aldehydes. However, the hydroformylation reaction of olefins (185) and the related oxo synthesis are effected by strong acid catalysts, eg, tetracarbonylhydrocobalt, HCo(CO)4 (see Oxo process). 

These reversible reactions are cataly2ed by bases or acids, such as 2iac chloride and aluminum isopropoxide, or by anion-exchange resias. Ultrasonic vibrations improve the reaction rate and yield. Reaction of aromatic aldehydes or ketones with nitroparaffins yields either the nitro alcohol or the nitro olefin, depending on the catalyst. Conjugated unsaturated aldehydes or ketones and nitroparaffins (Michael addition) yield nitro-substituted carbonyl compounds rather than nitro alcohols. Condensation with keto esters gives the substituted nitro alcohols (37) keto aldehydes react preferentially at the aldehyde function. 

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... 

Treatment of aromatic aldehydes such as p-anisaldehyde with Zn-powder and l,2-bis(chlorodimethylsilyl)ethane 45 give Zn-carbene adducts such as 2096 which add readily to olefins such as cyclohexene [22, 26] or styrene [26] to give high yields of cyclopropanes such as 2097 and the oxide 47 [26]. Acetals such as 2098 react analogously with cyclohexene to afford the endo and exo cyclopropanes 2099 and 2100 [22, 27] (Scheme 13.11). 

The asymmetric Baylis-Hillman reaction of sugar-derived aldehydes as chiral electrophiles with an activated olefin in dioxane water (1 1) proceeded with 36-86% de and in good yields of the corresponding glycosides (Eq. 10.47).104 The use of chiral /V-mcthylprolinol as a chiral base catalyst for the Baylis-Hillman reaction of aromatic aldehydes with ethyl acrylate or methyl vinyl ketone gave the adducts in good yields with moderate-to-good enantioselectivities in l,4-dioxane water (1 1, vol/vol) under ambient conditions.105... 

The criss-cross addition of azines of aromatic aldehydes with various electron-deficient olefins in which the double bond is terminal, for example, methyl acrylate, acrylonitrile, or in which allylic substituents do not sterically hinder the reaction, for example, maleic anhydride, is well known and was duly covered in CHEC-II(1996)<1996CHEC-II(8)747>, as well as in a review <1997ALD97>. Recently, the reaction has been used for the preparation of hyperbranched polymers <1998MI2655, 2002MAC712>. 

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... 

The same group recently disclosed a related free radical process, namely an efficient one-pot sequence comprising a homolytic aromatic substitution followed by an ionic Homer-Wadsworth-Emmons olefination, for the production of a small library of a,/3-unsaturated oxindoles (Scheme 6.164) [311]. Suitable TEMPO-derived alkoxy-amine precursors were exposed to microwave irradiation in N,N-dimethylformam-ide for 2 min to generate an oxindole intermediate via a radical reaction pathway (intramolecular homolytic aromatic substitution). After the addition of potassium tert-butoxide base (1.2 equivalents) and a suitable aromatic aldehyde (10-20 equivalents), the mixture was further exposed to microwave irradiation at 180 °C for 6 min to provide the a,jS-unsaturated oxindoles in moderate to high overall yields. A number of related oxindoles were also prepared via the same one-pot radical/ionic pathway (Scheme 6.164). 

ALDEHYDES FROM PRIMARY ALCOHOLS BY OXIDATION WITH CHROMIUM TRIOXIDE 1-HEPTANAL, 52, 5 ALDEHYDES FROM sym-TRITHIANE n-PENTADECANAL, 51, 39 Aldehydes, acetylenic, 54, 45 Aldehydes, aromatic, 54, 45 Aldehydes, benzyl, 54, 45 Aldehydes, olefinic, 54, 45... 

The dibromoalkene S-40 can be prepared from S-ethyl lactate by introduction of the MEM (methoxyethoxymethyl) protecting group, reduction to the O-protected lactaldehyde and Corey-Fuchs carbonyl olefination (Scheme 19). The l -enantiomer of 40 is available analogously from f -isobutyl lactate and serves as the reagent in the enantiomeric series. The lithium carbenoid S-41 is generated from S-40 by treatment with n-butyllithium in diethyl ether and reacted with aliphatic and aromatic aldehydes in tetrahydrofuran. High diastereoselectivities are reached, as shown in Scheme 19 . ... 

The product hydrazide may be sulfonated and decomposed by heating with a base in ethylene glycol to yield benzaldehyde, CeHsCHO. Many aromatic aldehydes may be produced by similar routes. The hydrazone derivative of toluenesulfonic acid reacts with an aldehyde or a ketone in the presence of a base catalyst, such as sodium ethoxide, to yield the corresponding olefin (Bamford-Stevens reaction) ... 

Urns-Epoxides. This unstable ylide (1), when generated as formulated above, reacts with an aliphatic aldehyde at —78° to give a fram-epoxide with almost complete stereoselectivity. The stereochemical selectivity is markedly dependent on the base and also on the counterion of the arsonium salt. Optimum selectivity for the trans-epoxide is obtained with conditions similar to those that induce cis-olefination in Wittig reactions.2 Stereoselection is not so high with aromatic aldehydes. The reagent also reacts with ketones to form trisubstituted epoxides. 

TPPMS serves as ligand in a variety of catalysts for hydrogenation,6 hydroformylation, and C-C bond formation.7 In aqueous solutions, it reacts with activated olefins,8 alkynes,9 and aliphatic as well as aromatic aldehydes,10 giving the corresponding substituted alkylphosphonium salts. 

Rhodium(II) acetate catalyzes C—H insertion, olefin addition, heteroatom-H insertion, and ylide formation of a-diazocarbonyls via a rhodium carbenoid species (144—147). Intramolecular cyclopentane formation via C—H insertion occurs with retention of stereochemistry (143). Chiral rhodium (TT) carboxamides catalyze enantioselective cyclopropanation and intramolecular C—N insertions of CC-diazoketones (148). Other reactions catalyzed by rhodium complexes include double-bond migration (140), hydrogenation of aromatic aldehydes and ketones to hydrocarbons (150), homologation of esters (151), carbonylation of formaldehyde (152) and amines (140), reductive carbonylation of dimethyl ether or methyl acetate to 1,1-diacetoxy ethane (153), decarbonylation of aldehydes (140), water gas shift reaction (69,154), C—C skeletal rearrangements (132,140), oxidation of olefins to ketones (155) and aldehydes (156), and oxidation of substituted anthracenes to anthraquinones (157). Rhodium-catalyzed hydrosilation of olefins, alkynes, carbonyls, alcohols, and imines is facile and may also be accomplished enantioselectively (140). Rhodium complexes are moderately active alkene and alkyne polymerization catalysts (140). In some cases polymer-supported versions of homogeneous rhodium catalysts have improved activity, compared to their homogenous counterparts. This is the case for the conversion of alkenes direcdy to alcohols under oxo conditions by rhodium—amine polymer catalysts... 

Fluorenylidene-(9)- (51, 55), carboalkoxymethylene- (28, 29, 48), acetylmethylene- (28, 29, 50), substituted benzoylmethylene- (28, 29, 56, 94) as well as Cv-nitrobenzylidene)- (58, 59, 97) -triphenylarsorane reacted with a variety of aromatic aldehydes to give corresponding olefins and triphenylarsine oxide. 

Reaction of benzylidene triphenylarsorane with aromatic aldehydes in alcohol afforded either arsine oxide and olefin or arsine and oxirane (97). Thus, from nitro- (58, 59, 97) or cyanobenzylidene derivatives (97) and aromatic aldehydes, trans-substituted oxiranes were obtained in 50-90% yield (97). Similarly, methylene triphenylarsorane reacted with benzal-dehyde in alcoholic solution to give triphenylarsine and phenyloxirane (49) in 87% yield (97). 

The benzylidene and p-chlorobenzyIidene triphenylarsorane ylides, when generated from sodium ethoxide in ethanol, react with a series of substituted benzaldehydes to give epoxides regardless of the nature of substituents present on the aromatic aldehyde (55, 97). However, the same ylides generated from sodium hydride in benzene (59), reacted with a series of aldehydes to give olefins. These observations clearly show that the base and solvent, in addition to the nature of substituent present on the ylidic carbanion, play an important role in dictating the exact path of the reaction. 

On the pages which follow, general methods are illustrated for the synthesis of a wide variety of classes of organic compounds including acyl isocyanates (from amides and oxalyl chloride p. 16), epoxides (from reductive coupling of aromatic aldehydes by hexamethylphosphorous triamide p. 31), a-fluoro acids (from 1-alkenes p. 37), 0-lactams (from olefins and chlorosulfonyl isocyanate p. 51), 1 y3,5-triketones (from dianions of 1,3-diketones and esters p. 57), sulfinate esters (from disulfides, alcohols, and lead tetraacetate p. 62), carboxylic acids (from carbonylation of alcohols or olefins via carbonium-ion intermediates p. 72), sulfoxides (from sulfides and sodium periodate p. 78), carbazoles... 

The reaction also proceeds efficiently with (Z)-enolates, as has been demonstrated with the trichlorosilyl enolate derived from propiophenone, (Z)-58 (Scheme 6.28). With aromatic and olefinic aldehydes the syn products syn-59-63 were formed as preferred diastereomers in high yields (89 to 97%) and with moderate to high syn/anti ratio (3.0 1 to 18 1). Enantioselectivity for the preferred syn diaster-... 

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