Andrea M. Aguilar

1,5-Asymmetric Induction in Boron-Mediated Aldol Reactions of β-Alkoxy Methylketones

Good levels of substrate-controlled, 1,5- syn-stereoinduction are obtained in boron-mediated aldol reactions of beta-trichloromethyl-beta-alkoxy and beta-trifluoromethyl-beta-alkoxy methylketones with achiral aldehydes, independent of the nature of the beta-alkoxy protecting group (TBS or PMB). In the case of boron aldol reactions of beta-aryl-beta-alkoxy methylketones, the 1,5- anti-adducts were obtained with high levels of diastereoselectivity only with a beta-OPMB group.

Indução assimétrica 1,5-Anti na adição de enolatos de boro de metilcetonas beta-oxigenadas a aldeídos

High levels of substrate-based 1,5-stereoinduction are obtained in the boron-mediated aldol reactions of b-oxygenated methyl ketones with achiral and chiral aldehydes. Remote induction from the boron enolates gives the 1,5-anti adducts, with the enolate p-facial selectivity critically dependent upon the nature of the b-alkoxy protecting group. This 1,5-anti aldol methodology has been strategically employed in the total synthesis of several natural products. At present, the origin of the high level of 1,5-anti induction obtained with the boron enolates is unclear, although a model based on a hydrogen bonding between the alkoxy oxygen and the formyl hydrogen has been recently proposed.

Recognition of Cyclic, Acyclic, Exocyclic, and Spiro Acetals via Structurally Diagnostic Ion/Molecule Reactions with the (CH3)2N-C+═O Acylium Ion

Reactions of the model acylium ion (CH3)2N-C(+)=O with acyclic, exocyclic, and spiro acetals of the general formula R(1)O-CR(3)R(4)-OR(2) were systematically evaluated via pentaquadrupole mass spectrometry. Characteristic intrinsic reactivities were observed for each of these classes of acetals. The two most common reactions observed were hydride and alkoxy anion [R(1)O(-) and R(2)O(-)] abstraction. Other specific reactions were also observed: (a) a secondary polar [4(+) + 2] cycloaddition for acetals bearing alpha,beta-unsaturated R(3) or R(4) substituents and (b) OH(-) abstraction for exocyclic and spiro acetals. These structurally diagnostic reactions, in conjunction with others observed previously for cyclic acetals, are shown to reveal the class of the acetal molecule and its ring type and substituents and to permit their recognition and distinction from other classes of isomeric molecules.

1,5-asymmetric induction in boron-mediated aldol reactions of beta-alkoxy methylketones

Good levels of substrate-controlled, 1,5- syn-stereoinduction are obtained in boron-mediated aldol reactions of beta-trichloromethyl-beta-alkoxy and beta-trifluoromethyl-beta-alkoxy methylketones with achiral aldehydes, independent of the nature of the beta-alkoxy protecting group (TBS or PMB). In the case of boron aldol reactions of beta-aryl-beta-alkoxy methylketones, the 1,5- anti-adducts were obtained with high levels of diastereoselectivity only with a beta-OPMB group.

1,5-asymmetric Induction In Boron-mediated Aldol Reactions Of β-alkoxy Methylketones

Good levels of substrate-controlled, 1,5- syn-stereoinduction are obtained in boron-mediated aldol reactions of beta-trichloromethyl-beta-alkoxy and beta-trifluoromethyl-beta-alkoxy methylketones with achiral aldehydes, independent of the nature of the beta-alkoxy protecting group (TBS or PMB). In the case of boron aldol reactions of beta-aryl-beta-alkoxy methylketones, the 1,5- anti-adducts were obtained with high levels of diastereoselectivity only with a beta-OPMB group.

1,5-asymmetric Induction In Boron-mediated Aldol Reactions Of Beta-oxygenated Methyl Ketones.

This tutorial review describes that high levels of substrate-controlled, 1,5-stereoinduction are obtained in the boron-mediated aldol reactions of beta-oxygenated methyl ketones with achiral and chiral aldehydes. Remote induction from the boron enolates gives the 1,5-anti adducts, with the enolate pi-facial selectivity critically dependent upon the nature of the beta-alkoxy protecting group. This 1,5-anti aldol methodology has been strategically employed in the total synthesis of several natural products with remarkable pharmacological activities. At present, the origin of the high level of 1,5-anti induction obtained with the boron enolates is unclear, although a model based on hydrogen bonding between the beta-alkoxy oxygen and the formyl aldehyde hydrogen has recently been proposed.

1,5-asymmetric Induction In Boron-mediated Aldol Reactions Of Beta-alkoxy Methylketones.

Good levels of substrate-controlled, 1,5- syn-stereoinduction are obtained in boron-mediated aldol reactions of beta-trichloromethyl-beta-alkoxy and beta-trifluoromethyl-beta-alkoxy methylketones with achiral aldehydes, independent of the nature of the beta-alkoxy protecting group (TBS or PMB). In the case of boron aldol reactions of beta-aryl-beta-alkoxy methylketones, the 1,5- anti-adducts were obtained with high levels of diastereoselectivity only with a beta-OPMB group.