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[reaction: see text] A catalytically active palladium-complexed tetracyclic N-heterocyclic carbene (NHC) was prepared in three steps from commercially available 1,10-phenanthroline by using a reduction-cyclization-deprotonation sequence. The new carbene framework is a prototype for the development of a series of chiral N-heterocyclic carbenes.

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LETTER 720Brønsted Acid Catalyzed Asymmetric Reduction of 2-and 2,9-Substituted 1,10-Phenanthrolines B r ø n s t e d A c i d C a t a l y z e d A s y m m e t r i c R e d u c t i o n o f 1 , 1 0 -P h e n a n t h r o l i n e s Abstract: Several 2-and 2,9-substituted 1,10-phenanthrolines are reduced asymmetrically for the first time using a Hantzsch dihydropyridine in the presence of BINOL-derived phosphoric acid catalysts. The best results are obtained with phenanthrolines bearing unbranched or nitrogen-containing alkyl groups in the 2-or 2,9-positions, which afford chiral octahydrophenanthrolines in a range of yields (40-88%) and good to excellent levels of enantiomeric purity (78-99% ee).Pioneering work by Akiyama 1 , Terada, 2 and others 3,4 has demonstrated the power of BINOL derivatives of phosphoric acid in Brønsted acid catalyzed asymmetric synthesis. Among the growing applications of this methodology is a report by Rueping 5 that 2-substituted quinolines can be reduced to tetrahydroquinolines (1 → 2, Scheme 1) in high enantiomeric purity with Hantzsch dihydropyridine 3 in the presence of catalysts 4a or 4b. 6 Although several other excellent methods have been developed for the asymmetric reduction of quinolines 7 and pyridines, 8 they involve less convenient high-pressure conditions (e.g. 1 → 5, Scheme 1), or they are not amenable to the reduction of substituted 1,10-phenanthrolines that are of interest to our group. 9,10

The biotransformations of a series of substituted phenylthio-2-propanone and benzylthio-2-propanone were carried out using Helminthosporium sp. NRRL 4671, Mortierella isabellina ATCC 42613, or Rhodococcus erythropolis IGTS8. Several products gave microbial oxidation of sulfide to sulfoxide and reduction of carbonyl to secondary alcohol, producing beta-hydroxysulfoxides in medium to high enantiomeric and diastereomeric purities. Fungal biotransformations using Helminthosporium sp. and M. isabellina resulted in the opposite sulfoxide configurations of various beta-hydroxysulfoxide products.