Nature employs dihydroxyacetone phosphate (DHAP) as the donor component in various enzyme-catalyzed aldol reactions. Probably the most significant example in this regard is photosynthesis, in which D-glucose, the most widespread natural product, is formed in just a few steps from DHAP. In recent years a number of synthetic equivalents of DHAP have been reported that deserve particular attention, as their applicability in organic synthesis is not limited to (stereoselective) aldol reactions. The power of these reagents has also been demonstrated convincingly in numerous other asymmetric electrophilic alpha-substitution reactions in target-oriented syntheses. Furthermore, the related 1,3-dioxins are useful equivalents of 2-substituted acrolein derivatives.

Treatment of trans-[NiF(2-C5F4N)(PEt3)2] (1), obtained by reaction of Ni(COD)2 with PEt3 and pentafluoropyridine, with Me3SiOTf effects the formation of the air-stable triflate complex trans-[Ni(OTf)(2-C5F4N)(PEt3)2] (2). The X-ray crystal structure reveals a molecular complex with approximately square-planar coordination at nickel, a Ni−O distance of 1.957(2) Å, and a Ni−C distance of 1.851(3) Å. The reaction of 2 with NaOPh yields the phenoxy complex trans-[Ni(OPh)(2-C5F4N)(PEt3)2] (3). The crystal structure of 3 was determined. The Ni−O and Ni−C distances are 1.894(4) and 1.861(6) Å, respectively. The complexes trans-[NiPh(2-C5F4N)(PEt3)2] (5) and trans-[NiMe(2-C5F4N)(PEt3)2] (6) were obtained on treatment of 1 with PhLi and Me2Zn, respectively. Treatment of 6 with CO yielded 2-acetyltetrafluoropyridine, while reaction with air yielded 2-methyltetrafluoropyridine. The studies reported in this paper demonstrate the synthesis of nickel derivatives of tetrafluoropyridine with the metal in a 2-position as well as the preparation of new 2-substituted tetrafluoropyridines by C−C coupling reactions.

The SAMP-hydrazone of 2,2-dimethyl-1,3-dioxan-5-one represents a valuable chiral dihydroxyacetone equivalent. Asymmetric mono-or a,a¢-bisalkylations followed by auxiliary cleavage leads to the corresponding mono-or a,a¢-disubstituted, acetonide protected ketodiols in excellent diastereo-and enantiomeric excesses.

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