Butanone equivalent

Swinholide A. The swinholides are a series of complex macrodiolides isolated from the marine sponge Theonella Swinhoei, which display potent cytotoxicity against a range of human tumour cell lines. Swinholide A (71) provided an excellent opportunity to showcase the synthetic utility of a range of aldol reactions. For its total synthesis by our group in 1994 [50] the fully protected preswinholide A 72 was considered to be an essential late-stage intermediate, which appeared accessible via two directed aldol reactions of a suitable butanone equivalent with aldehydes 73 and 74 (Scheme 9-24). 

With aldehydes 73 and 74 in hand, two alternatives were considered for the completion of the synthesis of preswinholide A, i.e. carrying out the butanone aldol reaction on either the methyl or the ethyl side first (see Scheme 9-24). Initially, the former option was investigated. While the reaction of the kinetic boron enolate of butanone with aldehyde 73 did not favour the desired Felkin adduct 83, the addition of allyl silane 84 (a masked butanone equivalent) proved selective in the desired sense (Scheme 9-27). This change in selectivity indicates the stereochemical reversal possible when switching from a cyclic to an acyclic transition state. 

Vbgtle and his coworkers have prepared a large number of compounds containing sulfur and nitrogen . An especially interesting type of compound is 11 which contains a pyridine subcyclic unit. This compound is prepared from one equivalent each of 2,2-dibromodiethyl ether and 2,6-dimercaptopyridine in a mixture of ethanol and 2-butanone. An excess (3 equivalents) of KOH served as base. Crystalline 11 (mp 168— 170°) was obtained in 9% yield. The approach is illustrated in Eq. (6.10). 

The water is added in order to hydrolyze the a-bromodimethyl ketals that have been produced during the reaction. The ease of hydrolysis of these bromoketals depends on the structure of the ketone. With aeetylcyclohexane (1-cyclohexylethanone) or acetylcyclopentane, stirring with water for 10 minutes is sufficient for complete hydrolysis. In contrast, with phenylacetone (1-phenylethanone) or methyl ethyl ketone (2-butanone), after dilution with water, the addition of 10 equivalents of concentrated sulfuric acid with respect to ketone and stirring for 15 hours at room temperature are necessary for complete hydrolysis. 

Horeau and co-workers (130) found that an ether solution containing four molar equivalents of (+ )-camphor added to one molar equivalent of LAH, followed by addition of A1C13, reduced 2-butanone or pinacolone. The reagent involved is presumably the same as that prepared by Eliel and Nasipuri (111), although the reaction leading to the formation of 111 is different (eq. [29]). The... 

The value of 6 mole % oxime ester was chosen. The data indicate, that poIy(methyl methacrylate-co-3-oximino-2-butanone methacrylate-co-methacrylonitrile) (P(M-OM-CN)) exhibits an 2.5 fold increase in sensitivity over the corresponding copolymer when the mole fraction of methacrylonitrile is 15-22%. On increasing this to 28%, the sensitivity begins to decrease. This latter effect is potentially due to the solubility characteristics of the polymer. Since the sensitivity of P(M-OM-CN) (86 6 8) is equivalent to that of P(M-OM) (94 6), it appears that a minimum amount of methacrylonitrile, between 8 and 15% in this instance, is required before any improvement in photosensitivity is observed. 

Pinacol rearrangement is a dehydration of a 1,2-diol to form a ketone. 2,3-drmethyl-2,3-butanediol has the common name pinacol (a symmetrical diol). When it is treated with strong acid, e.g. H2SO4, it gives 3,3-dimethyl-2-butanone (methyl r-butyl ketone), also commonly known as pinacolone. The product results from the loss of water and molecular rearrangement. In the rearrangement of pinacol equivalent carbocations are formed no matter which hydroxyl group is protonated and leaves. 

Just as there are enantiotopic and diastereotopic atoms and groups, so we may distinguish enantiotopic and diastereotopic faces in trigonal molecules. Again we have three cases (1) In formaldehyde or acetone (G), attack by an achiral reagent A from either face of the molecule gives rise to the same transition state and product the two faces are thus equivalent. (2) In butanone or acetaldehyde (H), attack by an achiral A at one face gives a transition... 

The intermediary cofactor bound acetyl anion equivalent can be transferred to an aldehyde acceptor, e.g. to acetaldehyde already produced during regular catalytic reaction in which optically active 3-hydroxy-2-butanone (acetoin, an important aroma constituent) is formed. Interestingly, PDCs from different sources differ in stereoselectivity [443] acetoin (I )-143 is obtained using brewer s yeast PDC (ee 28-54%) [444,445] while the enantiomeric (S)-143 is produced preferentially by PDC from wheat germ (ee 16-34%) [446] or from Z. mobilis (ee 24-29%) [445], When glyoxylate 14 (instead of 2) is subjected to decarboxylation in the presence of acetaldehyde, optically active lactaldehyde... 

Diazomethane is prepared as described in Org. Synth., Coll. Vol. /V1963, 250, with 50 g of Diazald (from Aldrich Chemical Company, Inc.) in 300 mL of ether added to 15 g of KOH in 25 mL of water, 30 mL of ether, and 50 mL of 2-(2-ethoxy-ethoxy)ethanol. One equivalent of diazomethane becomes incorporated in the reaction product, and the remainder serves as a scavenger for the HCI produced as a reaction by-product. The excess of diazomethane called for in this procedure is necessary to inhibit the undesired formation of 1-chloro-4-phenyl-2-butanone. The submitters report that this reaction can be performed on twice this scale with comparable results. 

Direct rearrangement to cyclobutanones can be achieved under four sets of conditions a) with 48% aqueous fluoroboric acid in ether, at room temperature b) with anhydrous stannic chloride in methylene chloride, normally at room temperature c) with p-toluenesulfonic acid in benzene saturated with water, at reflux and d) with trimethyloxonium tetrafluoroborate in methylene chloride (Meerwein s reagent). For instance, the cyclopropylcarbinol 233 was rearranged to 2-/-butyl-2-methylcyclo-butanone 235, upon treatment with one equivalent of pTsOH in water-saturated benzene at reflux for 1.5 hr, Eq. (72) 139). In a slightly different approach, the alcohol... 

When butanone was used as an extractant without preliminary use of chloroform, the polymer recovered was equal to the combined weights of I and II extracted separately from an equivalent sample. This was verified for many individual samples, using various additives. 

Splitting is not generally observed between protons separated by more than three a bonds. Although Hg and are not equivalent to each other in 2-butanone and ethyl methyl ether, and Hb are separated by four o bonds and so they are too far away to split each other s NMR signals. 

Trifluoro-2-oxopropanal l-(dimethylhydrazone) 1447 is a synthetic equivalent of trifluoropyruvaldehyde. Like its 1,2-dicarbonyl counterpart, compound 1447 participates in the condensation reaction with aldehydes and ammonium acetate to afford 4-trifluoromethylimidazoles 1448 in 42-72% yield <2003H(60)1185>. 1,1,1-Trifluoro-2,3-alkanediones 1449, also 1,2-dicarbonyl equivalents, condense with aldehydes and aqueous ammonia to yield 4-(trifluoromethyl)imidazoles 1450 <2001JHC773>. 3-(Dimethylhydrazono)-l,l,l,4,4,4-hexafluoro-2-butanone... 

A more typical result from the days before specific enol condensation between butanone and butanal with equivalents had been invented is this attempted crossed catalytic base. Two products were isolated in low yield. 

Addition of two equivalents of vinylmagnesium chloride in tetrahydrofuran to 2-hydroxycyclo-butanone gave cw-l-vinylcyclobutane-l,2-diol (6, 75%), exclusively, which on heating in chloroform containing a catalytic amount of boron trifluoride-diethyl ether complex, at reflux for five minutes, gave the 1-vinylcyclopropanecarbaldehyde (7), quantitatively. ... 

Fig. 2.16 Catalytic enantioselective Baeyer-Villiger oxidation of prochiral ketones, using H2O2 (in the form of a urea-adduct) as oxygen equivalent in stoichiometric amounts (a) 3-phenylcyclobutanone, (b) tricyclic cyclo-butanone.

An enzymic counterpart of these complex base-catalysed rearrangements of sugars may be the reaction catalysed by 4-phospho-3,4-dihydroxy-2-butanone synthetase. The enzyme catalyses the formation of the eponymous intermediate in secondary metabolism from ribulose 5-phosphate. Labelling studies indicated that C1-C3 of the substrate became C1-C3 of the product, that H3 of the substrate derived from solvent and that C4 was lost as formate. X-ray crystal structures of the native enzyme and a partly active mutant in complex with the substrate are available. The active site of the enzyme from Met ha-nococcus jannaschii contains two metals, which can be any divalent cations of the approximate radius of Mg " or Mn ", the two usually observed. Their disposition is very reminiscent of those in the hydride transfer aldose-ketose isomerases, but also to ribulose-5-phosphate carboxylase, which works by an enolisation mechanism, so the enolisation route suggested by Steinbacher et al. is repeated in Figure 6.14, as is the Bilik-type alkyl group shift, for which an equivalent reverse aldol-aldol mechanism cannot be written. 

As mentioned earlier, the increase in the in HTW and SCW produces equivalent quantities of and OH and therefore the increase in the observed rate of reaction could also arise from base catalysis. Eckert et al. observed base catalysis in HTW in the Claisen-Schmidt condensation of benzaldehyde and 2-butanone. The product outcome of this reaction under normal aqueous conditions depends upon whether the reaction is acid or base catalysed in acid catalysis a monosubstituted enone is formed whereas the base-catalysed route yields a disubstituted enone as the favoured product (Scheme 3.6). The disubstituted enone was found to be the dominant product for the Claisen-Schmidt condensation in HTW indicating base catalysis as the dominant pathway in HTW. 

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