Ketones naturally occurring

As solvents, the amyl alcohols are intermediate between hydrocarbon and the more water-miscible lower alcohol and ketone solvents. Eor example, they are good solvents and diluents for lacquers, hydrolytic fluids, dispersing agents in textile printing inks, industrial cleaning compounds, natural oils such as linseed and castor, synthetic resins such as alkyds, phenoHcs, urea —formaldehyde maleics, and adipates, and naturally occurring gums, such as shellac, paraffin waxes, rosin, and manila. In solvent mixtures they dissolve cellulose acetate, nitrocellulose, and ceUulosic ethers. 

According to Quinkert, photoexcited cyclic ketones may be transformed to open-chain unsaturated carboxylic acids in the presence of molecular oxygen. This reaction may compete efficiently with a-cleavage and secondary transformations thereof. Thus, both stereo iso meric 17-ketones (109) and (110) yield as much as 20% of the unsaturated acid (111) when irradiated in benzene under a stream of oxygen. This photolytic autoxidation has been used notably for partial syntheses of naturally occurring unsaturated 3,4-seco-acids from 3-oxo triterpenes (for references, see ref. 72). 

The solubility of most metals is much higher when they exist as organometallic complexes.4445 Naturally occurring chemicals that can partially complex with metal compounds and increase the solubility of the metal include aliphatic acids, aromatic acids, alcohols, aldehydes, ketones, amines, aromatic hydrocarbons, esters, ethers, and phenols. Several complexation processes, including chelation and hydration, can occur in the deep-well environment. 

The telomer of nitroethane, 134, was used for the synthesis of 11-hydroxy-8-frans-dodecenoic acid (135) (125). Apparently, the internal double bond of 134 must have a trans configuration from a mechanistic consideration. The nitro group was converted to alcohol via ketone, and the two-carbon homologation was carried out from the terminal double bond. This acid is converted to recifeiolide (136), a naturally occurring macrolide. 

Scheme 18.14 Naturally occurring glycosides ofthe grasshopper ketone-...

Pharmacologically active allenic steroids have already been examined intensively for about 30 years [5], Thus, the only naturally occurring allenic steroid 107 had been synthesized 3 years before its isolation from Callyspongia diffusa and it had been identified as an inhibitor of the sterol biosynthesis of the silkworm Bombyx mori (Scheme 18.34) [86d], At this early stage, allenic 3-oxo-5,10-secosteroids of type 108 were also used for the irreversible inhibition of ketosteroid isomerases in bacteria, assuming that their activity is probably caused by Michael addition of a nucleophilic amino acid side chain of the enzyme at the 5-position of the steroid [103, 104]. Since this activity is also observed in the corresponding /3,y-acetylenic ketones, it can be rationalized that the latter are converted in vivo into the allenic steroids 108 by enzymatic isomerization [104, 105],... 

An example of the method described is the synthesis of saphenic acid (47) that has recently been reported by Nielsen et al. [81]. Starting from properly substituted aromatic precursors 92 and 93, the naturally occurring 1,6-disub-stituted phenazine was synthesized in racemic form. Here, the first major step involves an intermolecular nucleophilic aromatic substitution that, due to the substitution pattern, has proved to be relatively unproblematic and after hydrolysis of the acetal yields the o-nitrodiphenylamine 94. Much more difficult is the ring formation leading to the final phenazine, which can best be achieved through a high excess of NaBH4, accompanied by reduction of the methyl ketone. But at 32%, the yield is still rather poor. 

Retrosynthetic analysis of 5 and 6 yielded ketone 7 as pivotal intermediate. A key reaction for the synthesis of 7 was the auxiliary-controlled, di-astereoselective biaryl coupling of a phenyl magnesium bromide (from 8 or 9) with aryloxazoline 10 (Scheme 1). This coupling strategy was developed in the Meyers laboratory [12] and previously applied to the enantioselective synthesis of other naturally occurring biaryl lignans, such as steganone [13]. 

The carbohydrates are a group of naturally occurring carbonyl compounds (aldehydes or ketones) that also contain several hydroxyl groups. The carbohydrates include single sugars (monosaccharides) and their polymers, the oligosaccharides and polysaccharides. 

Polycyclic oxasqualenoid glabrescol was synthesized by Corey and coworkers in order to confirm its structure. Several pentaoxacyclic compounds were synthesized via epoxidation with ketone 26 followed by cyclizations [90]. Finally, compound 48 was synthesized to match the properties of the naturally occurring glabrescol, leading to the determination of the stereochemistry of glabrescol (Scheme 7) [91]. 

Pattenden and Teague have prepared tricyclic diol 684 which is epimeric to the naturally occurring A < -capnellene-8p,10a-diol (68S) Their strategy, which is summarized in Scheme LXXI, encompasses two critical cyclization steps. The first is the Lewis acid-catalyzed ring closure of enol acetate 686 and the second involves reductive closure of acetylenic ketone 687. It is of interest that the oxidation of 688 proved to be stereospecific. 

Raspberry ketone [4-(4 -hydroxyphenyl)-butan-2-one], the impact compound found in raspberries, can be obtained by enzymatic reactions The first step is the /i-glucosidase-catalysed hydrolysis of the naturally occurring betu-loside to betuligenol. The latter can be transformed into raspberry ketone by microbial alcohol dehydrogenase (Scheme 22.2) [56]. 

---