Ketones, unsaturated reduction

Clemmensen reduction of aldehydes and ketones. Upon reducing aldehydes or ketones with amalgamated zinc and concentrated hydrochloric acid, the main products are the hydrocarbons (>C=0 —> >CHj), but variable quantities of the secondary alcohols (in the case of ketones) and unsaturated substances are also formed. Examples are ... 

TABLE 16. ORGANOSILANE REDUCTION OF a,p-UNS ATURATED KETONES (Continued) Unsaturated Ketone Conditions Product(s) and Yield(s) (%)... 

Unsaturated ketones of all kinds can be converted to saturated ketones, to unsaturated alcohols, to saturated alcohols, to alkenes and to alkanes. If the double bond is conjugated with the carbonyl group reduction usually takes place more readily and may give, in addition to the above products, e-diketones formed by coupling at j -carbons. 

Reduction of unsaturated ketones to unsaturated alcohols is best carried out Nit v complex hydrides. a,/3-Unsaturated ketones may suifer reduction even at the conjugated double bond [764, 879]. Usually only the carbonyl group is reduced, especially if the inverse technique is applied. Such reductions are accomplished in high yields with lithium aluminum hydride [879, 880, 881, 882], with lithium trimethoxyaluminum hydride [764], with alane [879], with diisobutylalane [883], with lithium butylborohydride [884], with sodium boro-hydride [75/], with sodium cyanoborohydride [780, 885] with 9-borabicyclo [3.3.1]nonane (9-BBN) [764] and with isopropyl alcohol and aluminum isopro-... 

Reduction of a, -unsaturated ketones to unsaturated hydrocarbon is rather rare, and is almost always accompanied by a shift of the double bond. Such reductions are accomplished in good to high yields by treatment of the p-toluenesulfonylhydrazones of the unsaturated ketones with sodium borohydride [785], borane [786] or catecholborane [559], or by Wolff-Kizhner reduction or its modifications [590]. However, complete reduction to saturated hydrocarbons may also occur during Wolff-Kizhner reduction [597] as well as during Clemmensen reduction [750]. 

The following tables are intended to include all the reductions with aluminum alkoxides which were reported prior to February, 1943, although some examples doubtless have been overlooked. Table I lists the reduction of aldehydes, which have been subdivided into (a) aliphatic aldehydes and (b) alicyclic and aromatic aldehydes. Table II lists the reduction of ketones, which have been classified as (a)-satu-rated and unsaturated aliphatic ketones, (b) aromatic ketones, (c) alicyclic ketones, (d) unsaturated alicyclic and aromatic ketones, (e) a- — halogen substituted ketones, (f) diketones, (g) protected diketones, (h) alcoholic and phenolic ketones (and ethers or esters of these), and (i) keto esters. 

Reductive dimerization of ketones Aromatic -unsaturated ketones are reduced and dimerized to 1,5-hexadienes by sequential reaction with LiAIH4, Fe3(CO)i2, and HCl. The effectiveness of iron carbonyls shows the order Fe3(CO), 2 > Fe2(CO)y > FeiCO). ... 

Enantioselective Ketone Reduction. After the pioneering work of Itsuno et al., Corey s group isolated the 1,3,2-oxazaborolidine derived from chiral a,a-diphenyl-2-pyrrolidinemethanol (2) and applied it (and also other related B-alkyl compounds) to the stereoselective reduction of ketones with borane-tetrahydrofuran, borane-dimethyl sulfide (BMS) or catecholborane.It was named the CBS method (after Corey, Bakshi, and Shibata). Since then, the CBS method has become a standard and has been extensively used, specially for aromatic and a,p-unsaturated ketones, not only in academic laboratories but also in industrial processes. ... 

All five Group I metals (Li, Na, K, Rb and Cs) and three Group II metals (Ca, Sr, Ba) have been used in NH3 to effect the reduction of ketones to secondary alcohols. " In addition, it has been reported that Yb-NH3 reduction of a,p-unsaturated ketones affords the saturated alcohol as the major product, which presumably arises via reduction of the intermediate saturated ketone.Reduction of (+)-camphor with Yb-NH3 both in the absence and presence of NH4CI affords the same 86 14 ratio of bomeol (2) to iso-bomeol (3). In the presence of NH4CI, the ketone is completely consumed and dimeric reduction products are not observed. Excess Yb-THF-HMPA effects bimolecular reduction of aromatic ketones, but aliphatic ketones are apparently inert to Yb-THF. - ... 

Cyclic, a, yS-unsaturated oximes, such as testosteronepropionate oxime, are reduced in two, two-electron steps in acid solution. The first reduction yields the imine, which is hydrolyzed to the unsaturated ketone. Reduction at the potential of the second wave yields the unsaturated amine [1]. 

Thebainone-B [xm] is best prepared as its hydrobromide by the hydrolysis of dihydrothebaine- [iv] with alcoholic hydrobromic acid [13], but it is also formed by the hydrolysis of the same base with mineral acid in aqueous solution [13], a reaction first reported to give an ill-defined substance, isocodeine [18], and later said to give a coloured, varnish-like substance [3]. Thebainone-B appears to be stable only as its salts in the dry state, the damp salts and free base readily degenerating to brown tars [13]. The ultra-violet spectra of thebainone-A, /3-thebainone-A, and thebainone-B closely resemble those of dihydrothebaine- and codeine, whilst that of thebainone-C is widely different (Fig. 8) and the frequencies of the carbonyl-absorption in the infra-red indicate that whereas thebainone-A and /3-thebainone-A are a /3-unsaturated ketones, the unsaturation is /3 y- in thebainone-B and thebainone-C [13]. On this evidence thebainone-B is allotted the structure [xm]. It can be catalytically reduced to dihydrothebainone [ix], in which the configuration at C-14 is the same as in codeine [13] (cf. the production of dihydrocodeine on reduction of neopine [xiv] [19]). 

Cyclopropanol Derivatives by Clemmensen and Related Reductions of a,/ -Unsaturated Ketones, a,/ -Unsaturated Aldehydes or 1,3-Diketones... 

Similarly, photogeneration of other reducing radicals results in reduction of diaryliodonium salts. Hydrogen abstraction from ethers and alcohols by ketone triplets [97], formation of 1,4-biradical by reaction of ketones with unsaturated compounds such as acrylates [97,103], all yield radicals which reduce diaryliodonium salts. Hydrogen atom abstraction from ethers and amines provides a chain process for iodonium salt decomposition (Scheme 6), wherein quantum yields as high as 5 have been reported [60a]. 

Several contributions have appeared in which intermolecular reductive couplings between ketones or aldehydes and electron-deficient alkenes have been described [30h, 53]. Reactions of aldehydes and ketones with unsaturated esters result in the formation of lactones. Diastereoselectivities are normally modest in these cases, but can be quite high for certain substitution patterns (Eq. 45). 

Reduction of a,p-unsaturated ketones. Reduction of an a,/3-unsaturated ketone in a fused ring system such as (1) with Raney nickel in 2 N NaOH and... 

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