of 600 mg 0 5 mmol of 4 34 5 di o t butyldimethylsilyl 7 o trimethysilyl 22 hydroxy 23 oxo avermectin b2a in 6 ml of benzene in an aluminum foil covered glass vial was added 400 mg 0 9 mmol of lead tetraacetate in one portion after 30 minutes at 20 u00b0 c the solution was poured into a separatory funnel containing 12 ml of water and 600 mg of sodium sulfite the mixture was then shaken and extracted with ethyl acetate the combined extracts were dried mgso 4 filtered and evaporated to afford 600 mg of solid flash chromatography through a column of silica gel eluting with 2 1 hexane ethyl acetate then acetone afforded 250 mg of starting material and 230 mg of aldehyde acid nmr u03b40 08 d j 6 hz 0 13 s 0 89 s 0 92 s 1 15 d j 6 hz 1 18 d j 6 hz 1 20 d j 6 hz 1 26 d j 6 hz 1 5 s 1 53 m 1 78 s 2 3 m 2 78 br s 3 13 t j 9 hz 3 23 t j 9 hz 3 23 s 3 32 s 3 36 m 3 42 br s 3 68 m 3 81 m 3 82 d j 6.