Hydroalkylation of olefins

An example of an intermolecular consecutive reaction is the hydroalkylation of olefins [139, 140]. Ti02 photocatalyzes the reaction of benzyltrimethylsilane... 

Oligomerizations, polymerizations and telomerizations are covered in other parts of this section, since C-C/C-C bond forming additions (dicarborations) are involved. Metal-mediated hydroalkylations of olefins with CH acidic compounds and hydroarylations with formal addition of aromatic C—H bonds to olefins are also known2, however, only a few examples of stereoselective applications have been reported (Section 1.5.8.2.6.). 

This method can be exploited as part of a one-pot hydroalkylation of an internal alkyne. Thus, titanium-catalyzed syn hydrozincation [24], followed by Negishi cross-coupling with an alkyl halide, stereospecifically generates a trisubstituted olefin (Eq. 8). 

Sames et al. reported a Sc(OTf)3-catalyzed intramolecular hydroalkylation of isolated electron-deficient olefins (Scheme 43) [95]. Tetrahydropyrans or tetrahy-drofurans carrying C(2)-Iinked a, P-unsaturated malonate side chain 109 and 111 were employed as substrate to furnish the spiroether product 110 and 112 in excellent yields. Notably, germinal substitution along the olefin tether was not required for efficient annulation for the reason that benzylidene malonate activated by Sc(OTf)3 were reactive enough, thus higher conformational rigidity to increase the reactivity of hydride acceptor was not indispensable [96]. 

This section summarizes the most studied organic reactions catalyzed by zeolites and mesoporous aluminosilicates useful in the synthesis of flavoring compoxmds, in perfumery, and other industrial fields. Acetalization reactions of aldehydes/ketones and the intramolecular hydroalkylation of xmsatxxrated alcohols or tandem reactions such as Claisen rearrangement and subsequent intramolecxxlar hydroxyalkylation of olefins are some of the noted reactions. 

Sames and coworkers have very recently introduced BF3 OEt2 catalysis to promote room temperature hydroalkylation of electron deflcient olefins as a formal sp C-H functionalization process. Coordination of the Lewis acid to the alkene moiety of the tetrahydropyran (121) facilitates a 1,5-hydride shift to afford a zwitterionic species, (122), which is followed by nucleophilic attack at the oxocarbonium center to furnish the requisite spirocyclic pyran (123) (Equation 74) [77]. 

A method for the preparation of alkanes in which alkylazodiphenylmethanols (5) decompose at 35—50 °C to hydroalkylate olefins has now been examined in detail. The yields, which are only moderate, can be improved by the addition of a hydrogen-atom donor (e.g. phenol). Unsymmetrical olefins are hydroalkyl-ated with the regiochemistry expected for a radical mechanism in which the alkyl radical adds first (Scheme 10). 

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