Aliphatic allylation

FIGURE 10. Voltammetric curves of fully aliphatic allylic sulphones (c = 3 x 10-3 M) in DMF/TBAP 0.1 m electrolyte, stationary mercury electrode, sweep rate 10 mV s—1 (a) and (b) curves in aprotic DMF (c) response of the sulphone, (b) with phenol 10-2 m (after Reference 26). 

We will describe representative procedures for the epoxidation of a disub-stituted aromatic allylic alcohol (A), a trisubstituted aromatic allylic alcohol (B) and a disubstituted aliphatic allylic alcohol (C). 

Grosjean, D Atmospheric Chemistry of Toxic Contaminants. 5. Unsaturated Halogenated Aliphatics Allyl Chloride, Chloro-prene, Hexachlorocyclopentadiene, Vinylidene Chloride, J. Air Waste Manage. Assoc., 41, 182-189 (1991c). 

The utility of the copper/Taniaphos-catalyzed allylic alkylation was further illustrated in two subsequent reports. The application of aliphatic allylic bromides containing protected alcohols and amines leads to the efficient synthesis of bifunctional building blocks (Scheme 15) . ... 

In sharp contrast to the reactivity of sulfur tetrafluoride (see Sections 8.1.-8.3,), (dia-lkylamino)lrifluoro->l4-sulfanes convert alcohols to their corresponding fluorides under mild conditions, generally at temperatures between room temperature and — 78 C. Aliphatic, allylic, acetylenic, benzylic, and amino alcohols have been converted to fluorides in good yields. 

Chemical Shift. The position of the resonance signal of a proton (or of a group of identical protons) is an indication of the molecular environment of that proton and permits, e.g., the distinction of aliphatic, allylic, olefinic, and aromatic hydrogens. 

The reaction is believed to proceed via a c-allyl copper complex, in which the carbon-copper bond is formed at the "/-position, anti to the acetate leaving group. Reductive elimination of copper led to pure "/-substitution. With cyclic aliphatic allylic acetates, the selectivity is generally lower because the o-allyl copper complex can isomerize to the ir-allyl complex with loss of regioselectivity. 

Three types of C-F bonds are encountered in unsaturated acids and their functional derivatives, namely nonactivated aliphatic, activated aliphatic (allylic, benzylic, and a to carbonyl), and vinylic bonds. The ease and selectivity of the reduction of C-F bonds is strongly dependent on the chemical environment. 

As can be seen from Table VI, secondary aliphatic, allylic, and benzylic alcohols are all quantitatively converted into the corresponding carbonyl derivatives. It is interesting to note that no epimeriza-tion of menthone takes place under these conditions (Entry 3). Furthermore, rather hindered decaline derivatives (Entry 5) are also smoothly oxidized. 

The regeneration of the benzoquinone can also be achieved with dioxygen in the absence of the cobalt cocatalyst. Thus, Hanyu et al. [86] showed that a combination of RuCl2(Ph3P)3, hydroquinone and dioxygen, in PhCF3 as solvent, oxidized primary aliphatic, allylic and benzylic alcohols to the corresponding aldehydes in quantitative yields (Eq. 20). 

Another improvement is the use of a Ru/TEMPO catalyst combination for the selective aerobic oxidations of primary and secondary alcohols to the corresponding aldehydes and ketones, respectively (Fig. 1.22) [72]. The method is effective (>99% selectivity) with a broad range of primary and secondary aliphatic, allylic and benzylic alcohols. The overoxidation of aldehydes to the corresponding carboxylic acids is suppressed by the TEMPO which acts as a radical scavenger in preventing autoxidation. 

A different example of gold-catalyzed alcohol activation is the silylation of primary alcohols. In this reaction, aliphatic, allylic, and benzylic primary alcohols undergo silylation with an Au(I)-xantphos chelated complex. ... 

The use of ether as solvent for thionyl chloride reactions apparently suppresses reactions by trapping hydrogen chloride in a non-ionic form, so that no Cl ions are available in solution [ig]. In certain aliphatic allylic alcohols solvent changes can have a profound effect on product composition, but no comparable data are available for steroid reactions. 

The reaction of the analogous aliphatic allyl ethers is stereoselective, an observation first applied to the synthesis of trans-trisubstituted olefins, in particular squalene (see Scheme 19.2). 

Hiersemann, M., Abraham, L. Catalysis of the Claisen rearrangement of aliphatic allyl vinyl ethers. Eur. J. Org. Chem. 2002, 1461-1471. 

H-(3-zeolite, anisole, toluene, reflux, 1.5-8 h, 70-90% yield. Cinnamyl esters are also cleaved in excellent yield, but allyl esters give mixed results with aliphatic allyl esters showing no cleavage. ... 

Publications on CPO-catalyzed oxidations of alcohols are rare. However, some selective oxidations of aliphatic, allylic, propagylic and benzylic alcohols to the aldehyde stage have been reported (Table 16.2-11). 

A number of primary and secondary aliphatic, allylic, and benzylic alcohols could be selectively converted to the corresponding carbonyl compounds within 2 hours reaction time, and with excellent isolated yields ranging from 71 to 97 % as listed in Table VI 88). 

An IBX-mediated conversion of primary alcohols (or aldehydes) into A-hydroxysuccinimlde esters 848 has been developed by Giannis and coworkers [1164]. The generality of this procedure was demonstrated on various aliphatic, allylic and benzylic alcohols (Scheme 3.338). 

---