Transformations of the Carbonyl Functions

Diphenylcyclopropene thione (156) was prepared11S-12°) from 3,3-dichloro-1,2-diphenyl cyclopropene (154) by reaction with thioacetic acid, since transformation of the carbonyl function of diphenyl cyclopropenone with P4S10121 was complicated by ring expansion to the trithione 155122 In a useful recent thioketone synthesis123) 156 was obtained directly from diphenyl cyclopropenone in a quantitative yield by simultaneous treatment with HC1 and H2S. 

It has been reported that the distannoxanes can also promote transformation of the carbonyl function, e.g. esterification [333b], lactonization [340a], polymerization [340 b, c], acetahzation [341], deacetalization [342], and desilylation [342] as well as transesterification, and in each reaction the mild conditions enable survival of a variety of acid-labile functions. With recourse to organotin-catalyzed transesterification, a variant of deacylation can be performed under mild conditions while conventional deacylation demands acidic or basic conditions. When l,n-diol diacetate was treated... 

However, the radical addition of p-chlorobenzotrichloride on dimethylpentene ester failed. The longer sequence of Lewis-acid-catalyzed addition of benzoylchloride, transformation of the carbonyl function 225 in the chloroolefine 226 and subsequent ring closure gives the whole set of possible isomers 227. Only the trans-Z is the one of interest. 

Hydrogenation of the carbonyl function is an important synthetic transformation and can be catalyzed by complexes of several transition metals including -among others- Co, Rh, Ru, Ir, and Os. In aqueous organometallic catalysis the first examples were given by the hydrogenation of water-soluble 2-oxo-carboxylic acids, 1,3-dihydroxyacetone and fmctose [47-54], later the same substrates were also used for testing new catalysts [29]. 

Transformations of the nitro function in 142 to a carbonyl group employing variants of the Nef reaction or its reduction to a cyclic nitrone 143, which is capable to undergo 1,3-dipolar cycloadditions, underscore the high synthetic potential of these nitroalkane adducts (Eq. 62)84). 

It has been shown in the preceding Sections that the reactivity of various carbonyl-containing phosphoranes provides a direct avenue to introduction of the carbonyl function in a sugar molecule. There is, however, an alternative mode of such transformation that consists in introduction of such carbonyl precursors as enol, thioenol, or enamino groupings, provided that appropriate ylides (149) are available and that the final products may be converted into carbonyl compounds under mild conditions. 

It will be instructive to comment briefly on the outcome of compound XIV, whose difference with respect to intermediate IV is the nonquatemization of the amine portion. Although the result of its exposure to II is the same in that tricyclic compound XVIII is produced, the amino-Claisen rearrangement cannot account for this process, since the protonation that would be expected to occur at nitrogen, thereby triggering the concerted transformation, surprisingly takes place instead on the oxygen atom of the carbonyl function (see Scheme... 

As is the case for oxycyclopropanes extra activation and extended product functionality is achieved by using sulphur-substituted cyclopropanes with a vicinal acceptor group. According to equation 116 synthesis of a variety of y-oxothioesters and j -oxoketene dithioacetals is possible. A formylcyclopropane of this type has been converted to a furan derivative " . Transformation of the carbonyl to a hydroxymethyl group and acid treatment allows preparation of dienes " ... 

Tensile extensibility is a particularly sensitive measure of the extent of weathering. Alternatively, the development of carbonyl functionalities (>C=0) or other spectral changes in samples determined in Fourier Transform Infra-Red Spectroscopy, FTIR, might be used to assess degradation, hi PE (Andrady et al., 1993b), the development of the carbonyl functionalities correlates well with the decrease in extensibility. Plastics such as PVC, PC, or PS (Ghaffar et al., 1976) turn yellow on photodegradation. Surface... 

Photochemical changes in both II and the acetoxy derivative have been monitored in fluid solution and incorporated in a polymer film. Fig. 5 shows the spectral changes accompanying photochemical transformation of the acetoxy derivative. Then changes may be interpreted in terms of scheme 3, which proposes a photochemical 1,3 acyl shift to form "in situ" an ultraviolet stabilizer chromophore which also has a carbonyl functionality. 

Reduction to Alkanes. Carbonyl groups can be reductively deoxygenated to methylene functions if both of the two steps represented by Eqs. 1 and 2 proceed to completion. With aldehydes, this process leads to the transformation of the CHO group into a CH3 group. 

Coriolin (689), a metabolite of the Basidiomycete Coriolus consors, has attracted widespread interest because of its unusual anti-tumor activity and highly functionalized triquinane structure. Accordingly, a number of syntheses of689 have appeared on the scene. One of the earliest, due to Tatsuta, et al., begins with epoxide 690, whose preparation had been earlier realized in connection with their work on hirsutine (see Scheme LXIII). Deoxygenation of 690, hydrolysis, and cis-hydroxy-lation provided keto triol 691 (Scheme LXXII) The derived acetonide was transformed via 692 into tetraol 693 which could be selectively acetylated and dehydrated on both flanks of the carbonyl group. Deacetylation of 694 followed by epoxidation completed the synthesis. 

When the C—H bond to be oxidized is proximate to a functional group, as we have stated already, its reactivity depends on the type of functional group. In the case of the hydroxy group, especially in secondary alcohols, these are more prone to dioxirane oxidation than their alkane precursors and, consequently, usually carbonyl products are obtained as the final product. Primary alcohols are less reactive, but may still be converted slowly to the corresponding aldehydes or carboxylic acids (due to the facile further oxidation of aldehydes)The functional-group transformation of the alcohols to ethers or acetals reduces the oxidative reactivity " but these C—H bonds are still more reactive than unfunctionalized ones. Thus, dioxirane oxidation of benzyl ether or acetal may... 

All the reactions described above rely on the electrophilic reactivity of the carbonyl C atom of the aldehyde 2. Much effort was devoted to the development of phosphaferrocenes with nucleophilic reactivity at this position. For example, transformation of the formyl group into a halomethyl function would pave the way for the preparation of Grignard or lithium derivatives by halogen-metal exchange. However, all attempts to do this were unsuccessful. 

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