Desymmetrizing Hydroformylation of Dialkenylcarbinols with the Aid of a Planar-Chiral, Catalyst-Directing Group

Total Synthesis of (-)-Cylindrocyclophane F: A Yardstick for Probing New Catalytic C-C Bond-Forming Methodologies

A short and efficient total synthesis of the C₂ -symmetric (-)-cylindrocyclophane F is presented, using a cross olefin metathesis dimerization strategy for construction of the [7,7]-paracyclophane macrocycle. The synthesis of the dimerization building block includes a Pd-catalyzed sp³ -sp² Negishi cross coupling of a sterically hindered Zn-reagent with an aromatic triflate, an enantiospecific Zn-catalyzed sp³ -sp³ cross coupling of an α-hydroxy ester triflate with a Grignard reagent and the application of an enantioselective Rh-catalyzed C-allylation of an electron rich arene.

Desymmetrizing Hydroformylation of Dihydromuconic Acid Diesters: Application to the Synthesis of (±)-Vindeburnol

The desymmetrizing hydroformylation of internal alkenes derived from dihydromuconic acid is described. The study of this reaction afforded easy access to polyfunction aldehydes. After the evaluation of the reactivity of the dimethyl ester derivative with various primary amines, this methodology was used to design a rapid synthesis of (±)-vindeburnol from tryptamine in only two steps.

Chiral Ligands for Rhodium-Catalyzed Asymmetric Hydroformylation: A Personal Account

Asymmetric hydroformylation represents one of the most efficient routes for the preparation of chiral aldehydes from alkenes in the presence of syngas in a perfect atom-economic way. During the past few decades, a variety of chiral ligands have been developed for the asymmetric hydroformylation. However, only a few ligands exhibit good performance in terms of the regio- and enantioselectivities. Additionally, for the chiral ligands developed up to now, only limited substrates were tolerated and no examples have led to the application of the asymmetric hydroformylation reaction on a commercial scale due to several technical challenges. This account provides a brief introduction of the current efficient chiral ligands for asymmetric hydroformylation and the ongoing efforts we have made in this field.

Structural characterization of O- and C-glycosylating variants of the landomycin glycosyltransferase LanGT2

The structures of the O-glycosyltransferase LanGT2 and the engineered, C-C bond-forming variant LanGT2S8Ac show how the replacement of a single loop can change the functionality of the enzyme. Crystal structures of the enzymes in complex with a nonhydrolyzable nucleotide-sugar analogue revealed that there is a conformational transition to create the binding sites for the aglycon substrate. This induced-fit transition was explored by molecular docking experiments with various aglycon substrates.

Regioselective hydroformylation of allylic alcohols

A highly regioselective hydroformylation of allylic alcohols is reported toward the synthesis of β-hydroxy-acid and aldehyde products. The selectivity is achieved through the use of a ligand that reversibly binds to alcohols in situ, allowing for a directed hydroformylation to occur. The application to trisubstituted olefins was also demonstrated, which yields a single diastereomer product consistent with a stereospecific addition of CO and hydrogen.

Removable directing groups in organic synthesis and catalysis

Directing groups have been widely used in recent years to achieve control over all aspects of reaction selectivity in a wide range of transformations involving transition-metal catalysis and organometallic reagents. In cases when the existing functional group within a substrate is unsuited to achieve efficient intramolecular delivery of a reagent or catalyst, the specific introduction of an appropriately designed removable reagent-directing group can be a solution to this problem. In this Review we give an overview of the state of the art in this area, including the stoichiometric and catalytic use of directing groups.

Synthesis of quaternary carbon centers via hydroformylation

The application of hydroformylation to the synthesis of quaternary carbon centers is reported. The synthesis of the highly substituted carbon is achieved by applying a catalytic amount of 1. Ligand 1 serves as a catalytic directing group by covalently and reversibly binding to both the substrate and catalyst. The intramolecular nature of the directing group strategy accelerates the hydroformylation reaction such that the reaction is performed at mild temperatures (35-55 degrees C) and with excellent regioselectivity (b:l > 94:6).

Enantioselective synthesis of 2,6-dideoxy carbasugars based on a desymmetrizing hydroformylation-carbonyl ene cyclization process

A practical one-pot process involving a desymmetrizing hydroformylation with the aid of a chiral catalyst-directing group (CDG*), followed by a carbonyl ene cyclization provides a straightforward access to both enantiomers of the resulting cyclohexanediol; further divergent, highly selective and protecting group-free transformations furnish the carbocyclic analogues of four important 2,6-dideoxysugars.