Versatile roles of Lewis acids in the reactions of allylic tin compounds

Cobalt- and rhodium-catalyzed cross-coupling reaction of allylic ethers and halides with organometallic reagents

Mechanistic studies on the B(C6F5)3 catalyzed allylstannation of isomeric substituted benzaldehydes are reported. Confirming a report by Maruoka et al., good (5:1) to excellent (>20:1) selectivities for ortho over para isomers are observed when 1:1 mixtures (X = OMe, Cl, F, OTBS) are allylstannated with C3H5SnBu3 in the presence of B(C6F5)3 (2.5% per CHO). The best selectivities are observed for the anisaldehydes. Multinuclear NMR studies on solutions of B(C6F5)3 and C3H5SnBu3 (1:1 to 1:5) show that the borane abstracts the allyl group from the organotin reagent, forming an adduct (C6F5)3B···CH2CHCH2SnBu3, 1, or ion pair [(C6F5)3BCH2CHCH2]-[Bu3SnCH2CHCH2SnBu3]+, 2, depending on the reagent ratio. These compounds are important in the mechanism of Lewis acid catalyzed 1,3-isomerization of substituted allyl stannanes. When allyltin reagent is added to solutions of B(C6F5)3 and ortho-anisaldehyde (1:5) at −60 °C, conversion to the stannylium ion pair [Bu3Sn(ortho-anisaldehyde)2]+[o-ArCH(allyl)OB(C6F5)3]-, o,o...

Mechanistic Studies on the B(C6F5)3 Catalyzed Allylstannation of Aromatic Aldehydes with Ortho Donor Substituents

3.4 – Transition Metal Alkyl Complexes: Oxidative Addition and Transmetallation

Organotin homoenolate equivalents - access to β-acyl-and β-aryl-propionaldehydes through heterosubstituted allyltins and vinyltins

Selectivity in reactions involving α-alkoxyallyltributyltins

α-ETHOXYBUTENYLTRIBUTYLTIN PRECURSORS OF α-ETHOXYBUTENYLLITHIUM: APPLICATION TO THE SYNTHESIS OF ENONES VIA HOMOALLYL MONOETHERS OF α-GLYCOLS

The behaviour of α-alkoxyallyltributyltins has been studied in terms of chemo-, regio- and stereoselectivity. Chemoselectivity is readily controlled by the experimental conditions, as exemplified by the reaction of p-bromobenzaldehyde with α-ethoxycrotyltributyltin. Cross-coupling products are the sole products when the reaction is catalyzed by Pd(PPh3)4 while the use of Lewis acids, or even simple heating of the reagents, cause addition to the aldehyde group.

The regio and stereochemistries of the addition reactions can also be controlled in some circumstances. For instance, the BF3. Et2 O promoted reactions (CH2 Cl2, −78°C) lead regio- and stereoselectively to the α -glycol monoether 16E (93 % syn E). On the other hand, the (E)-α-ethoxycrotyltributyltin has been shown to be much more reactive than the (Z)- isomer. It allows highly regio and stereoselective reaction affording 19Z (anti Z) on heating (100°C, 6 h).

These results are discussed and an interpretation of the stereochemical trends is given on the basis of the interactions occurring in usually accepted transition states.

B. Elissondo

Papers

Selectivity in reactions involving α-alkoxyallyltributyltins

α-ETHOXYBUTENYLTRIBUTYLTIN PRECURSORS OF α-ETHOXYBUTENYLLITHIUM: APPLICATION TO THE SYNTHESIS OF ENONES VIA HOMOALLYL MONOETHERS OF α-GLYCOLS

Selectivity in Reactions Involving α-Alkoxyallyltributyltins.