Aldehydes from lactones

Aldehydes react with dimethyl 2-phenylselenofumarate (70) at -70 °C in diethyl ether in the presence of MeLi to give good yields of highly substituted 4-phenylselenobutano-y-lactones (71) and (72). High diastereoselectivity [for benzaldehyde, (71) (72)-89 11] was rationalized by assuming the formation of a chelated intermediate between MeLi and (70), with approach of the aldehyde from the favoured si-fact (Scheme 5). " ... 

Reduction of lactones leads to cyclic bemiacetals of aldehydes. With a stoichiometric amount of lithium aluminum hydride in tetrahydrofuran at —10° to —15° and using the inverse technique, y-valerolactone was converted in 58% yield to 2-hydroxy-5-methyl tetrahydrofuran, and a-methyl-5-caprolac-tone in 64.5-84% yield to 3,6-dimethyl-2-hydroxytetrahydropyran [1028]. Also diisobutylaluminum hydride in tetrahydrofuran solutions at subzero temperatures afforded high yields of lactols from lactones [7024]. 

Molasses. A large number of volatile and nonvolatile compounds have been identified in the flavor fractions of various types of molasses (51-621. Compound classes identified include aliphatic and aromatic acids, aldehydes, phenols, lactones, amines, esters, furans, pyrazines, and sulfides. Most of these compounds can arise from carbohydrate degradation through a number of traditional pathways especially because residual nitrogen-containing sources are present. 

Esters and lactones can be partially reduced with the participation of a single hydride. Starting from esters, aldehydes are formed via the corresponding hemiace-tals. Starting from lactones, the products are generally lactols (Figure 3.51). 

The lactone 145, obtained from lactone 144 in two steps, gave upon reduction, followed by mesylation and selective displacement of the primary O-mesyl group with azide ion, the azide 146. Reductive cyclization and benzylation of 146 furnished 147, whose primary hydroxyl group was oxidized to produce the aldehyde 148. On the other hand, protection of... 

An efficient process for the synthesis of a,/3-epoxy-aldehydes from a ,j3-unsaturated acids has been reported.The acid (62) is converted into the bromo-lactone [64 = a- or 3-Me, = Ph or (CH2)sMe or R R =... 

Looking carefully at the current literature we have learned that the ketene dithioacetal chemistry, widely used for one-carbon homologation of carbonyl compounds, has never been utilized for the construction of ulosonic acids [129]. Besides, ketene dithioacetals, readily available from ketones and aldehydes via the reaction with the ylides generated from substituted dithioacetals in the Peterson, Wittig or Homer-Emmons olefmation, have never been synthesized from lactones. 

Oak from different origins is odoriferous to varying degrees. Its characteristic odors are mainly revealed during seasoning and barrel manufacture. Heating (Section 13.8.3) forms furanic derivatives, volatile phenols and phenylketones, as well as increasing concentrations of phenol aldehydes and lactones. 

Several quinones have been identified by Soxhlet extraction of atmospheric particulate material, including anthraquinone and more complex multi-ring compounds (Choudhury, 1982 Ramdahl et al., 1982). In addition, more than 40 other oxygenated PAHs including aldehydes, ketones, lactones, and anhydrides have also been characterized from airborne particle extracts (Choudhury, 1982 Newton et al.. 

The routes leading from lactone A have the advantage of a chiral source of starting materials. With the two chiral centers at C24 and C25 set, the problem reduces down to elaborating the B ring with the appropriate substituents. An early solution was provided in an unusual cyclization of the B ring via an intramolecular Michael addition to the unsaturated aldehyde formed from a nitrile oxide 1,3-dipolar cycloaddition to the allyl methyl ketal of lactone A [76]. This clever use of relative stereocontrol provided by the highly constrained and predictable transition states of both key reactions unfortunately resulted in a low yield. A more conventional approach conceptualized the addition of a sulfoxide [77] to 2 to yield a masked diol-ketone precursor which cyclizes under acidic catalysis. Elimination of the sulfoxide permitted the introduction of the hydroxy substituent at C19 of the spiroketal. 

Lactone products can also be formed via Grignard-type addition to aldehydes from o-iodobenzoates [116]. The Cheng group developed an enantioselective Co-catalyzed method for preparation of 5-membered phthalide products from methyl o-iodobenzoate and aldehydes (Scheme 2.61). While Ni and Pd catalysts were ineffective, the authors propose a Co(I)/Co(III) mechanism involving oxidative addition of the sp C—I bond followed by addition and ring closure [116]. Co(III) is reduced to Co(I) by the zinc metal present in solution. 

Under the influence of the triamine-Al catalyst, in situ generated ketene (formed from acyl bromide and diisopropylethy-lamine) reacted with aliphatic or aromatic aldehydes, affording -lactone in excellent yield and 88 96% ee (eq 5). AAC reactions deliver enatioeniiched -lactone acetate aldol surrogates, which are direct progenitors of numerous chiral building blocks (/S-amino acid, allene, and Q , -disubstituted carboxylic acids ). 

Hydrogenation in alcoholic acid converts ketones into ethers Good yields of aldehydes from esters as well as hydroxyaldehydes from lactones can be obtained by reduction with NaAlH4 at low temp. The preparation of aldehydes under mild conditions by cleavage of p-dimethylaminophenlycarbinols with diazotized sul-... 

The reaction of enolates derived from lactones (121) with aromatic aldehydes has been used effectively in the synthesis of lignan lactones, e.g. (122) and... 

Sodium tetrahydridoaluminate Aldehydes from carboxylic acid esters Hydroxyaldehydes from lactones... 

Fat is, on the one hand, a source of taste and aroma compounds and, on the other, a medium that regulates the distribution of these compounds between water, fat and vapour phases, which influence their perception by the sense organs. Some flavour compounds result from the decomposition of lipids by lipolysis, oxidation (section 3.3.4), and microbial or thermal degradation. These processes may produce free fatty acids, aldehydes, ketones, lactones and other volatile compounds (Figure 5.10). 

Silyl enol ethers are other ketone or aldehyde enolate equivalents and react with allyl carbonate to give allyl ketones or aldehydes 13,300. The transme-tallation of the 7r-allylpalladium methoxide, formed from allyl alkyl carbonate, with the silyl enol ether 464 forms the palladium enolate 465, which undergoes reductive elimination to afford the allyl ketone or aldehyde 466. For this reaction, neither fluoride anion nor a Lewis acid is necessary for the activation of silyl enol ethers. The reaction also proceed.s with metallic Pd supported on silica by a special method[301j. The ketene silyl acetal 467 derived from esters or lactones also reacts with allyl carbonates, affording allylated esters or lactones by using dppe as a ligand[302]... 

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