Procedure:  50 mL 1-neck flask, stirbar

                  Dissolved 0.430 g of I in 12 mL of CH₂Cl₂ and 3.0 mL of 2.5 M methanolic NaOH.  Stirred at -78 C.  Ozone was passed through the solution which became yellow.  After 65 min, the solution became blue and a yellow precipitate had formed.  The reaction mixture was diluted with ether and water and allowed to warm to rt.  The layers were separated and the organic layer was dried over MgSO₄, filtered, and the solvent was removed by rotary evaporation.  The product was isolated by flash chromatography on silica gel using 1:9 EtOAc-hexanes as eluant.  The product was a clear, colorless oil. 

 

¹H NMR (CDCl₃, 500 MHz) d 7.32 (m, C₆H₅), 4.68, 4.38 (ABq, J = 11.7 Hz, CH₂Ar), 3.92 (t, J = 6.4 Hz, H2), 3.73 (s, CO₂CH₃), 1.77-1.23 (m, CH₂s), 0.86 (bt, J = 6.7 Hz, CH₃). 

 

notes

 

Ozonolysis of alkenes in methanolic NaOH and CH₂Cl₂ at low temperature affords methyl esters (see a) Marshall, J.A.; Garofalo, A.W.  J. Org. Chem.  1993, 58, 3675.  b) Jumnah, R.; Williams, J.M.J.; Williams, A.C.  Tetrahedron Lett.  1993, 34, 6619.  c) Pearson, W.H.; Jacobs, V.A.  Tetrahedron Lett.  1994, 35, 7001).  This reaction can often be used to avoid the multi-step sequence: ozonolysis of the alkene to the aldehyde followed by oxidation to the acid and esterification.  The postulated mechanistic pathway is shown below.  Formation of the secondary ozonide, VII, is substate dependent.  Unhindered olefins are more likely to produce amounts of secondary ozonides.  This procedure has been shown not to affect the stereochemistry at C2.