TADDOL

Structural formula
Left the (4 R , 5 R ) TADDOL, right the (4 S , 5 S ) TADDOL
General
Surname	TADDOL
other names	Seebach reagent (4 R , 5 R ) -TADDOL (4 R , 5 R ) -2,2-dimethyl-α, α, α ', α'-tetraphenyl-dioxolane-4,5-dimethanol (4 S , 5 S ) -TADDOL (4 S , 5 S ) -2,2-dimethyl-α, α, α ', α'-tetraphenyl-dioxolane-4,5-dimethanol
Molecular formula	C 31 H 30 O 4
Brief description	yellowish solid
External identifiers / databases
CAS number 93379-48-7 (4 R , 5 R ) -2,2-dimethyl- α, α, α ', α'- tetraphenyl-dioxolane-4,5-dimethanol 93379-49-8 (4 S , 5 S ) -2,2-dimethyl- α, α, α ', α'- tetraphenyl-dioxolane-4,5-dimethanol Wikidata Q2383523
properties
Molar mass	466.57 g mol −1
Physical state	firmly
Melting point	192-195 ° C
solubility	almost insoluble in water, soluble in chloroform
safety instructions
GHS labeling of hazardous substances no GHS pictograms H and P phrases H: no H-phrases P: no P-phrases
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

TADDOL (systematic name: α, α, α´, α´-tetraaryl-1,3-dioxolane-4,5-dimethanol), more precisely TADDOLs, are derivatives of tartaric acid , whereby the aryl radical is usually a phenyl radical . In modern asymmetric organic synthesis , they serve as chiral reagents for performing enantioselective reductions of ketones . Either (4 R , 5 R ) -2,2-dimethyl-α, α, α ', α'-tetraphenyldioxolane-4,5-dimethanol or (4 S , 5 S ) -2,2-dimethyl-α , α, α ', α'-tetraphenyldioxolane-4,5-dimethanol used, both enantiomers are commercially available. (4 S , 5 S ) -2,2-dimethyl-α, α, α ′, α′-tetra (1-naphthyl) -1,3-dioxolane-4,5-dimethanol (CAS No. 171086-52-5) and (4 S , 5 S ) -2,2-dimethyl-α, α, α ′, α′-tetra (2-naphthyl) -1,3-dioxolane-4,5-dimethanol ( CAS No. 137365-16-3), which contain 1-naphthyl or 2- naphthyl radicals instead of phenyl radicals . The TADDOLs are also known as Seebach reagents , named after the chemist Dieter Seebach .

Reactions

Using a complex of two equivalents each of LiAlH ₄ , ethanol and 2,2-dimethyl-α, α, α ', α'-tetraphenyldioxolane-4,5-dimethanol, aryl alkyl ketones can be reduced to secondary alcohols in high yields . This reduction is highly enantioselective. Depending on the ketone used, enantiomer ratios of up to 95: 5 can be achieved. With subsequent recrystallization from n- pentane , the selectivity could be increased to 97: 3, but the yield decreased dramatically.

Thus, the reduction of acetophenone with (4 R , 5 R ) -2,2-dimethyl-α, α, α ', α'-tetraphenyldioxolane-4,5-dimethanol -LiAlH ₄ - ethanol complex 1-phenylethanol with a Enantiomeric ratio of 95 ( S ): 5 ( R ) with a chemical yield of 95%.

The reason for the selectivity is the steric hindrance between the chiral reagent and the substrate molecule. When (4 R , 5 R ) -2,2-dimethyl-α, α, α ', α'-tetraphenyldioxolane-4,5-dimethanol is used, the corresponding ( S ) alcohol is usually formed as the reduction product of the asymmetrical ketone .

Individual evidence

1. ↑ ^{a b c d} TADDOL data sheet (PDF) from Merck , accessed on January 18, 2011.
2. ↑ Data sheet (4R, 5R) -2,2-Dimethyl-α, α, α ′, α′-tetraphenyldioxolane-4,5-dimethanol from Sigma-Aldrich , accessed on June 16, 2011 ( PDF ).
3. ↑ Dieter Seebach et al .: Reduction of Ketones with LiAlH4 Complexes of α, α, α ', α'-Tetraaryl-1,3-dioxolane-4,5-dimethanols (TADDOLs) A Combination of Enantioselective Reduction and Clathrate Formation with a Discussion of LAH Reagents Bearing C2-Symmetrical Ligands . In: Croatica Chem. Acta . 69, 1996. pp. 459-484. ( PDF , 9 MB).