Aldehydes double allylation

Double Allylation of Aldehydes with Dienes Promoted by Indium(I). 182... 

The synthetic utility and generality of the reaction is demonstrated by an intramolecular/intermolecular double allylation using an oo-dienyl aldehyde 38 as a probe. The internal diene terminus selectively undergoes nucleophilic allylation intramolecularly to form a cyclopentanol structure. The terminal... 

Iridium,204,205 together with osmium, has been not widely used in catalytic hydrogenation. Recently, however, iridium or iridium-based catalysts have been shown to be effective in various hydrogenations, such as in selective hydrogenation of a,P-unsaturated aldehydes to allylic alcohols (Section 5.2), of aromatic nitro compounds to the corresponding hydroxylamines (Section 9.3.6), of halonitrobenzenes to haloanilines without loss of halogen (Section 9.3.2), and in the stereoselective hydrogenation of carbon to carbon double bonds (see, e.g., eqs. 3.25-3.27 and Table... 

It is very well known that jr-allyl palladium complex 1, which is a key intermediate for the Tsuji-Trost type allylation, has an electrophilic character and reacts with nucleophiles to afford the corresponding allylation products. We discovered that bis 7r-allyl palladium complex 2 is nucleophilic and reacts with electophiles such as aldehydes [27] and imines [28-32] (Scheme 2, Structure 2). We have also shown that bis 7r-allyl palladium complex 2 can act as an amphiphilic catalytic allylating agent it reacts with both nucleophilic and electrophilic carbons at once to produce double allylation products [33]. These complexes incorporate two allyl moieties that can bind with different hapticity to palladium (Scheme 3). The different complexes may interconvert by ligand coordination. The complexes 2a, 2b and 2c are called as r]3,r]3-bisallypalladium complex (also called bis-jr-allylpalladium complex), r)l,r)3-bis(allyl)palladium complex, -bis(allyl)palladium complex, respectively. Bis zr-allyl palladium complex 2 can easily be generated by reaction of mono-allylpalladium complex 1 and allylmetal species 3 (Scheme 4) [33-36]. Because of the unique catalytic activities of the bis zr-allyl palladium complex 2, a number of interesting cascade reactions appeared in the literature. The subject of the present chapter is to review some recent synthetic and mechanistic aspects of the interesting palladium catalyzed cascade reactions which in-... 

Addition to aldehydes. The allylic tin reagent reacts with aldehydes in the presence of BF, ctherate to give preferentially the. vvn-homoallylic alcohol regardless of the geometry of the double bond (10, 411). When carried out in the absence of a catalyst but under high pressure, the reaction results mainly in the a/it/ -isomer. 

In accordance with this model one finds diastereoselectively anti products on reaction of aldehydes with ( )-allyl compounds, whereas allyl systems with the (Z)-configuration give mainly syn products and it is even possible to effect asymmetric induction. As the double bond of the product can be oxidatively cleaved to a CW3 group, the reaction can be regarded as a stereoselective aldol reaction, an aspect which explains the widespread interest in this type of reaction. With heterosubstituted allylic anions it is sometimes possible to effect predominantly y-attack with different electrophiles by the choice of the heteroatom.2 For instance it is well known that with sulfur substituents like —SR, —SOR or —SOjR the a-attack dominates, but doubly lithiated allenethiol possesses high y-reactivity and can be used as a homoenolate anion equivalent in reaction with electrophiles such as alkyl halides (Scheme 7). ... 

A new simple synthetic route to 2,5-dihydrooxazoles 71 by cycloaddition of allyl azido ethers 70 via triazoUnes was shown by Hassner et al. [37]. Earlier, they demonstrated that cr-azido ethers can be easily prepared from aldehydes using an alcohol, hydrazoic acid and titanium tetracliloride as well as the fact that thermolysis of azido ethers in the absence of a double bond forms imi-dates [35,36]. Using the above mentioned facts, the allyl azido ethers 70 were synthesized in good yields employing an aldehyde, an allyl alcohol and HN3 in a 1 3 9 ratio in presence of a Ti catalyst (Scheme 12). Allyl azido ethers 70, on thermolysis in benzene, proved to be ideal substrates for the formation of 2,5-dihydrooxazoles 71 in 66-90% yield. To show that oxazolines are formed via triazolines and not via an independent nitrene pathway, thermolysis of 70 was followed by NMR in hexadeuteriobenzene at 70 °C. 

In 2007, Hall and coworkers have disclosed a new family of simple and efficient double allylating reagents of type (11) as stable bimetallic reagents for stereoselective allylation reaction of aldehydes (Scheme 1.16) [22]. 

Chiral hydroxyl-functionalized allylic silanes were obtained by the reaction of various aldehydes and chiral double allylating reagent (11) with high enantioselec-tivities (up to 98% ee) and excellent E/Z ratio ( > 25 1 to > 30 1) using 1 equivalent of BP3 OEt2 as a Lewis acid promoter. The resulting chiral allylic silanes can be... 

Scheme 1.16 Asymmetric allylation of aldehydes with a new double-allylation reagent (11).

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