Journal of Organometallic Chemistry 581 (1999) 66 – 69 Application of 1,2:5,6-di-O -cyclohexylidene-D-mannitol as the chiral director in Matteson’s asymmetric homologation Guisheng Li, George W. Kabalka * Departments of Chemistry and Radiology, The Uniersity of Tennessee, Knoxille, TN 37996 -1600, USA Received 2 July 1998; received in revised form 3 September 1998 Abstract 1,2:5,6-Di-O-cyclohexylidene-D-mannitol is the good chiral director in Matteson’s asymmetric homologation as indicated by the high enantiomeric excesses (ee’s) of the secondary alcohols produced by treatment of the homologation products with alkyllithium or Grignard reagents followed by oxidation. © 1999 Elsevier Science S.A. All rights reserved. Keywords: Boronates; 1,2:5,6-Di-O-cyclohexylidene-D-mannitol; Homologation 1. Introduction Asymmetric homologation via -chloroboronic esters provides an extremely efficient method for constructing chiral centers [1]. The reaction has been extensively employed in syntheses of biologically important molecules including pheromones [2], homoallylic alco- hols [3], sugars [4], amino acids [5] and aminoboronic acids [6]. Pinanediol is often used as the chiral director but the hydrolytic stability of pinanediol boronates is problematic in some syntheses. The lack of C 2 symme- try is another disadvantage associated with pinanediol and it accounts for the poor diastereoselectivities ob- served in the reactions of pinanediol dichloromethyl- boronate with organolithium or Grignard reagents. To circumvent these difficulties, C 2 symmetric 1,2-diols are being developed as chiral ligands. Diacetone mannitol and tartrates [7] are ineffective but (R,R )-2,3-butanediol gives satisfactory results when used as the chiral direc- tor [8]. 1,2-Di-isopropylethanediol [9] and 1,2-dicyclo- hexylethanediol [1c,d, 3c] are also effective chiral directors, providing diastereomeric purities in excess of 98%. However, these chiral diols (1 and 2) are either expensive or are not yet commercially available. In light of the fact that the enantioselectivity in- creases as the size of the substituent increases in 2a – c, we felt that the C 2 symmetric 1,2:5,6-di-O -cyclohexyli- dene-D-mannitol, 3, which is sterically similar to 2b and is commercially available at a modest price, might serve as an effective chiral director. We wish to report the results of an investigation in which 3 was used as the chiral director in asymmetric homologation reactions. 2. Results and discussion The starting 1,2:5,6-di-O -cyclohexylidene-D-mannitol boronic esters, easily prepared via the quantitative reac- tions of the corresponding boronic acids and 3, are stable in air and can be purified by column chromatog- raphy on silica gel to give crystalline solid products in 90–95% isolated yields. In order to evaluate 3 as the chiral director in asymmetric homologations, a series of reactions (scheme) were carried out under conditions similar to those described by Matteson [2b]. Preformed * Corresponding author. Tel.: +1-423-9743260; fax: +1-423- 9742997. 0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII:S0022-328X(99)00066-2