BINOL: A Versatile Chiral Reagent

TADDOLs, which contain two adjacent diarylhydroxymethyl groups in a trans relationship on a 1,3-dioxolane ring, can be prepared from acetals or ketals of tartrate esters by reaction of the latter with aromatic Grignard reagents. They are extraordinarily versatile chiral auxiliaries. Here, a historical review of the subject is followed by discussion of the preparation of TADDOLs and analogous systems, including TADDOLs with N-, P-, O-, and S-heteroatom ligands appropriate for metals. Crystal structure analysis reveals that the heteroatoms on the diarylmethyl groups are almost always in close proximity to each other, joined together by H-bonds, and predisposed to form chelate complexes in which the metallic centers reside in propeller-like chiral environments. Applications of TADDOL derivatives in enantioselective synthesis extend from utilization as stoichiometric chiral reagents or in Lewis acid mediated reactions, to roles in catalytic hydrogenation and stereoregular metathesis polymerization. Derivatives and complexes based on the following metals have so far been investigated: Li, B, Mg, Al, Si, Cu, Zn, Ce, Ti, Zr, Mo, Rh, Ir, Pd, Pt. The number of stereoselective reactions already accomplished with TADDOLs is correspondingly large. It is also easy to prepare TADDOL derivatives that are readily polymerizable and graftable, and to transform them into immobilized solid-phase catalysts. The result is catalysts, simply or dendritically immobilized in polystyrene or on silica gel and characterized by unexpected stability even after multiple use in titanium TADDOLate mediated reactions. TADDOLs show further unusual characteristics that make them useful for applications in material science and supramolecular chemistry: they are the most effective doping agents known for phase transformations of achiral (nematic) into chiral (cholesteric) liquid crystals. The TADDOL OH group that is not involved in intramolecular H-bonding shows a strong tendency to associate intermolecularly with H-bond acceptors. In the process of crystallization this leads, enantioselectively, to the formation of inclusion compounds that lend themselves to the separation of racemic mixtures not otherwise suited to the classical method of crystallization through diastereomeric salts. The high melting points of TADDOLs even make possible the resolution of racemates by distillation! Host-guest compounds formed between TADDOLs and achiral partners can serve as platforms for enantioselective photoreactions. It seems safe to predict that many more applications will be discovered for the TADDOLs and their derivatives. Supporting information for this article is available on the WWW under http://www.angewandte.com or from the author.

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TADDOLs, Their Derivatives, and TADDOL Analogues: Versatile Chiral Auxiliaries

Enantioselective Gold Catalysis: Opportunities Provided by Monodentate Phosphoramidite Ligands with an Acyclic TADDOL Backbone

Update 1 of: BINOL: A Versatile Chiral Reagent

Atropisomerically pure (S)-4-phenyl-4,5-dihydro-3H-dinaphtho[2,1-c;1′,2′-e]phosphepine 2b has been obtained by resolution of the racemic compound with an enantiopure palladium complex and its absolute configuration has been determined by X-ray analysis; it is an effective chiral ligand for the asymmetric hydroformylation of styrene with rhodium catalysts.

Novel atropisomeric phosphorus ligands : 4,5-dihydro-3H-dinaphtho[2,1-c;1',2'-e]phosphepine derivatives

The chiral dithiepine 3 was selectively oxidized to all possible oxides: the sulfoxide 9, the sulfone 16, the sulfone-sulfoxide 20, the disulfoxide 21, and the disulfone 22. The sulfinyl oxygens of 9, 14, 20, and 21 are always in the pseudoaxial configuration, as shown by the X-ray structure determination of 11a. Reaction of the anions of 3, 9, and 16 with methyl iodide, benzaldehyde, or acetophenone occurs efficiently. The stereoselectivity of the processes is high and maximized in sulfoxide 9, where the contributions of the chiral binaphthyl residue and the sulfoxide appear to occur synergistically. The alcohols derived from reaction of the anions of 3, 9, and 16 with benzaldehyde and acetophenone were also prepared in high yield and stereoselectivity via reduction or methylation of the phenyl ketone 8 and of its oxidized homologues 14 and 19. Alcohol 6a, prepared in 8.2 ratio in the reaction of 3 with benzaldehyde, was obtained as a single diastereoisomer in the reduction of 8 with lithium aluminum hydride

Asymmetric reactions of thioacetals and their S-oxides derived from 1,1'-binaphthalene-2,2'-dithiol

Arylglyoxals, protected at the aldehyde function with 1,1′-binaphthalene-2,2′-diol, are readily prepared by direct nucleophilic substitution of binaphthol-sodium salt on dibromoacetophenone and react highly diastefeoselectively with lithium aluminium hydride and Grignard reagents to afford protected atrolactaldehyde and related compounds in high yield.

P. Maglioli

Papers

Asymmetric reactions of thioacetals and their S-oxides derived from 1,1'-binaphthalene-2,2'-dithiol

Highly diastereoselective reduction and addition of nucleophiles to binaphthol-protected arylglyoxals

A rapid preparation of 2,2′-dimercaptobiphenyl

Synthesis and Reactions of a Homochiral Hydroxythiol Derived from Tartaric Acid

Asymmetric Reactions of Thioacetals and Their S‐Oxides Derived from 1, 1′‐Binaphthalene‐2,2′‐dithiol.