Ketones, preparation from alcohols

Analogously, poly(vinyl ketals) can be prepared from ketones, but since poly(vinyl ketals) are not commercially important, they are not discussed here. The acetalization reaction strongly favors formation of the 1,3-dioxane ring, which is a characteristic feature of this class of resins. The first of this family, poly(vinyl ben2al), was prepared in 1924 by the reaction of poly(vinyl alcohol) with ben2aldehyde in concentrated hydrochloric acid (2). Although many members of this class of resins have been made since then, only poly(vinyl formal) [9003-33-2] (PVF) and poly(vinyl butyral) [63148-65-2] (PVB) continue to be made in significant commercial quantities. 

Fig (5) The ketoalcohol (34) prepared from ketone (33) has been converted to methoxyabietatriene(38), by standard organic reactions. Hydroboration, oxidation of (38), followed by oxidation, yielded the ketone (39), which is converted to the alcohol (40), by metal hydride reduction. On subjection to transanular oxidation with lead tetracetate and benzene alcohol (40) fiimishes (41) whose conversion to pisiferic acid has already been described. 

Aldehydes and ketones undergo catalytic hydrogenation using hydrogen gas under pressure and a metal catalyst such as nickel. Primary alcohols result from the hydrogenation of aldehydes and secondary alcohols are prepared from ketones. 

Ketone 72 (R = H) is iodinated in the 3-position by I2-HI03-H2S04.294 Attempts to prepare 4,5-dihydrobenzo[i>]thiophene by dehydration of the alcohol obtained from ketone 72 (R = H) were unsuccessful.300 However, this labile alkene has been obtained (72%) by vacuum pyrolysis of 1-(2-thienyl)buta- 1,3-diene.3 03... 

The structure of ( —) 2P-acetoxy-1 la-hydroxyverrucosane (544) was established as follows (Scheme 65). Jones oxidation of (544) gave a five-membered ketone (551). Acid treatment of the latter resulted in homoallylic ring expansion to homo-allylic ketoalcohol (552) which was converted via the tosylhydrazone into (548) identical with the homoallylic alcohol prepared from (547) via (545) (Scheme 64). That the 11-hydroxyl group was a was inferred from the remarkable downfield shifts exhibited by the C-10 and the C-12 methyl groups of the five-membered ketone (551) and the small solvent shift exhibited by the C-10 methyl group (553) and its homoallylic ring expanded product. 

Alcohols are prepared from aldehydes and 2° alcohols are from ketones. 

Ethyl a-naphthylacetate is prepared as follows. To a solution of 10 g. of the diazo ketone in 150 ml. of ethanol at 55-60°, add a small amount of aslurry of silver oxide, prepared from 10 ml. of 10 per cent, aqueous silver nitrate and stirred with 25 ml. of ethanol. As soon as the evolution of nitrogen subsides, introduce more of the silver oxide and continue the process until all the slurry has been added. Reflux the mixture for 15 minutes, add 2-3 g. of decolourising carbon, filter and evaporate the alcohol on a water bath. Distil the residue and collect the ethyl a-naph-thylacetate at 176-178°/ 1 mm. the yield is 9 g. 

The Dess-Martin periodinane ( DMP ) reagent, U,l-tris(acetyloxy)-l,l-dihydro-l,2-benziodoxol-3(l//)-one, has also been used in several complex syntheses for the oxidation of primary or secondary alcohols to aldehydes or ketones, respectively (e.g., M. Nakatsuka, 1990). It is prepared from 2-iodobenzoic add by oxidation with bromic add and acetylation (D.a Dess, 1983). 

Alkyl-2-arylthiazoles and 4,5-disubstituted-2-(p-aminophenyl thiazoles were simflarly prepared from arylamides and a-halomethyl-ketones in alcoholic (239, 392, 641, 792) or acetonic solution (638, 651). 

Alcohols can be prepared from carbonyl compounds by reduction of aide hydes and ketones See Table 15 3... 

Cross-conjugated dienones are quite inert to nucleophilic reactions at C-3, and the susceptibility of these systems to dienone-phenol rearrangement precludes the use of strong acid conditions. In spite of previous statements, A " -3-ketones do not form ketals, thioketals or enamines, and therefore no convenient protecting groups are available for this chromophore. Enol ethers are not formed by the orthoformate procedure, but preparation of A -trienol ethers from A -3-ketones has been claimed. Another route to A -trien-3-ol ethers involves conjugate addition of alcohol, enol etherification and then alcohol removal from la-alkoxy compounds. 

The requisite starting cyanohydrin is readily prepared from a 20-keto-pregnane substitution at C-21 has no effect on the success of this step. However, the stability of the cyanohydrin is markedly dependent on other features of the molecule thus a 3-acetate confers greater stability than the free alcohol, and a 3-ketone is so unstable that subsequent dehydration with phosphorus oxychloride gives poor yields of the A -unsaturated nitrile. 

The nitrites aie most conveniently prepared from the corresponding alcohols by treatment with nitrosyl chloride in pyridine. The crude nitrites can be precipitated by addition of water and recrystallized from appropriate solvents. However nitrites prepared from carbinols in which the adjacent carbon is substituted by halogen, free or esterified hydroxyl or a carbonyl function are very readily hydrolyzed and must be recrystallized with great care. In general the photolysis gives higher yields if purified and dried nitrites are used which do not contain acids or pyridine, although occasionally the addition of small amounts of pyridine is recommended in order to prevent hydrolysis of the nitrite. Traces of acids do in fact catalyze the thermal decomposition of secondary nitrites to equimolar amounts of alcohol and ketone. ... 

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)... 

The position of equilibrium is favorable for acetal fonnation from most aldehydes, especially when excess alcohol is present as the reaction solvent. For most ketones the position of equilibrium is unfavorable, and other methods must be used for the preparation of acetals from ketones. 

Tertiary alkoxyenyne alcohols 114, easily prepared from alkoxyenynes and ketones by the Favorsky reaction (74ZOR1835), give, with hydrazine and alkylhy-drazines in an acidic medium, 3(5)-substituted dialkylvinylpyrazoles 115 in 80% yield(81H146). 

Piperitone can be most easily obtained from the higher boiling portions of the oil of E. dives. It combines slowly with sodium-bisulphite, and by repeated agitation for two or three weeks eventually forms crystals in some quantity. A proportion of alcohol assists the combination. The pure ketone prepared from the purified crystals is colourless at first, but on long standing becomes slightly yellowish in tint. It has a burning peppermint-like taste and odour. The formula is... 

Alcohols occupy a central position in organic chemistry. They can be prepared from many other kinds of compounds (alkenes.. alkyl halides, ketones, esters, and aldehydes, among others), and they can be transformed into an equally wide assortment of compounds (Figure 17.3). 

Butylcyclohexanol has been prepared from />-/-butylphenol by reduction under a variety of conditions.3 4 Winstein and Holness5 prepared the pure trans alcohol from the commercial alcohol by repeated crystallization of the acid phthalate followed by saponification of the pure trans ester. Eliel and Ro 6 obtained 4-f-butylcyclohexanol containing 91% of the trans isomer by lithium aluminum hydride reduction of the ketone. Iliickel and Kurz 7 reduced />-/-butylphenol with platinum oxide in acetic acid and then separated the isomers by column chromatography. 

Although this material contains a small amount of the symmetrical dihydrazide, which is not easily eliminated on crystallization, it is entirely satisfactory for use as a reagent for the isolation of ketones. A purer product, m. p. 192°, with decomposition, can be obtained by adding the solution prepared from ethyl chloroacetate and trimethylamine to an alcoholic solution containing a considerable excess of the hydrazine hydrate. 

---