Methylene compounds regioselectivity

Grubbs et al. reported that the ruthenium-catalyzed RCM of a conjugated diene proceeds in such a way that the less hindered olefin moieties participate in the reaction. Consequently, RCM of 115 gives exo-methylene compound 116, and not exo-vinyl compound 117 (Scheme 24) [105]. This regioselectivity is complementary to that observed for enyne metathesis of 118, which gives exclusively 117 (Scheme 24) [106a]. 

The phosphine oxide (-)-(5 )-[2-(dimethylamino)ethyl]methyloxophenylphosphorane85 was treated with butyllithium or LDA to give, via directed lithiation, the methylene-deprotonated compound regioselectively. Alkylation with bromomethylbenzene gave (S)-[l-benzyl-2-(di-methylamino)ethyl]methyloxophenylphosphorane with low diastereoselectivity (d.r. 55 45)86. 

Intramolecular carbometallation of active methylene compounds having allenyl group proceeds in a complete regioselectivity in the presence of SnCl4 and Et3N to give a cyclohexene derivative (Equation (109)).278... 

As depicted in Equation (118), the regioselective addition of an active methylene compound to 2,3-dihydrofuran was promoted by catalytic amounts of AuClj-AgOTf, providing a 2-substituted THE as the product <20050L673>. 

Keywords Aldehydes, active methylene compounds, Bestmann-Ohira reagent [dimethyl(dia-zomethyl)phosphonate], potassium hydroxide, methanol, room temperamre, Knoevenagel condensation, one-pot multicomponent reaction, click chemistry, cycloaddition, phospho-nates, regioselective synthesis, phosphonyl pyrazoles... 

Sosnovskikh VY, Irgashev RA, Kodess MI (2008) One-pot three-component reaction of 3-(polyfluoroacyl)chromones with active methylene compounds and ammonium acetate regioselective synthesis of novel R -containing nicotinic acid derivatives. Tetrahedron 64 2997-3004... 

Notably, this methodology can be used for the regioselective CDC reaction of toluene derivatives with activated methylene compounds. Using the system [FeC (10 mol%), ( BuOO Bu) (2 equiv.), toluene, 120 °C for 24 h], 41% of the allq lated 1,3-dicarbonyl compound was obtained. The best catalytic system was based on Fe(OAc)2 (10 mol%) in combination with 4 equiv. of BuOO Bu (Scheme 4.5). 

Condensation of azides and appropriate activated methylene compounds is the method of choice to prepare in a regioselective manner 5-heterosusbtituted triazoles. For instance, reaction of benzyl azide 17 with ethyl cyanoacetate, cyanoacetamide, or cyanoacetic acid 18 in basic alcoholic solution delivered the corresponding l-benzyl-4-substituted-5-amino-l,2,3-triazoles or l-benzyl-4-substituted-5-hydroxy-l,2,3-triazoles 19 (Scheme 5) [34, 35]. Sometimes, care... 

Various terminal allylic compounds are converted into l-alkenes at room temperature[362]. Regioselective hydrogenolysis with formate is used for the formation of an exo-methylene group from cyclic allylic compounds by the formal anti thermodynamic isomerization of internal double bonds to the exocyclic position[380]. Selective conversion of myrtenyl formate (579) into /9-pinene is an example. The allylic sulfone 580 and the allylic nitro compound... 

Meldrum s acid, like other 1,3-dicarboxyl compounds, was amenable to radical reactions at C-5. The radical reaction between Meldrum s acid benzyl alkyl ethers mediated by InCl3/Cu(OTf)2 has been reported to proceed regioselectively at the benzylic position of the ether moiety (Scheme 35) <2006AGE1949>. Radical reaction of Meldrum s acid and alkenes was carried out with 2equiv of ceric ammonium nitrate (CAN) to give the a-carboxy-lactones which were subsequently subjected to decarboxylative methylenation affording the a-methylene lactones in 35-50% yield (Scheme 35) <2006SL1523>. 

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