Knowledge Economy : Textbook

Pyrethroid insecticides Chapter IVa. Reactivity of chrysanthemic acid and its lower esters

“…42 It is usually achieved with 2N aqueous solution of sodium or potassium hydroxides in refluxing methanol for 1.5-4 h (See below, Scheme 62). [43][44][45][46][47] Saponification of ethyl chrysanthemate (trans/cis: 90/10) has been also performed using 5 equivalents of potassium hydroxide in aqueous ethanol (EtOH/H2O; 5/1) at 135°C for 3 h and delivers stereoselectively chrysanthemic acid (86%, trans/cis: 90/10). 11 Even under these drastic conditions, saponification is faster than epimerization that would have led to cis/trans epimerization.…”

“…The vinylcyclopropane carboxylates needed for the process have been prepared independently (Section 2.1.1.) by reaction of the acid with a base (Scheme 35) 47,71,95 or in-situ in the presence of triethylamine (Scheme 36, entry a). 25 The reaction proved particularly well suited to produce benzylic or allylic esters on alkylation with benzyl- 25,47,71,90,95,96 or allyl-98 halides (Scheme 35, entries a,b,d, Scheme 36) or sulfonates (Scheme 35, entry c) as well as with allethronyl mesylate (see below, Scheme 38, entry b,c).…”

“…Synthesis of benzyl-and allyl-vinylcyclopropane carboxylates from their metal salts and related halides and sulfonates. 47,71,95,98 The reaction carried out with potassium carbonate under phase transfer catalysis 99,100 such as tetrabutyl ammonium bromide (TBAB) in dichloromethane proved highly efficient (Scheme 36, entries b-e). 25,96 Scheme 36.…”