Reactions of Vinylcyclopropane Epoxides with Samarium and Phosphorus Iodides

Abstract

Samarium diiodide on one hand, diphosphorus tetraiodide, and phosphorus triiodide on the other, react with vinylcyclopropane epoxides to produce either allylic alcohols or vinylcyclopropanes resulting from cyclopropane ring-opening or deoxygenation of the epoxide, respectively.We recently described 1 that ethyl oxido-chrysanthemate 1a is not, as expected, deoxygenated to ethyl chrysanthemate 2a by samarium diiodide, 2a-e the 'Kagan reagent' 2f in the presence of tert-butyl alcohol, but instead mainly produces 3a resulting from cyclopropane ringopening (Scheme 1, Table 1, entry a).Scheme 1 Reaction of samarium diiodide with vinylcyclopropane epoxides bearing an ester or a phenyl group on the cyclopropane ring We therefore initiated a study aimed to understand the reasons which favor (i) the participation of the cyclopropane ring after the samarium diiodide initiated epoxide ring-opening, (ii) the regioselectivity of the cleavage of the cyclopropane ring.We first confirmed that the conditions used are mandatory for success and that the presence of tert-butyl alcohol (2.5 equiv) is strictly required. 3 Surprisingly, it neither takes place in the presence of HMPA or DMAE (dimethylaminoethanol) which are known to enhance the reducing ability of samarium diiodide. 2

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

“…Otherwise oxido-chrysanthemic acid (16aH) derived from chrysanthemic acid (1aH) 217 (Scheme 103, entries a,b) and oxido-chrysanthemates (16aR) derived from its alkyl esters such as methyl (1aMe) , ethyl (1aEt) (Scheme 103, entries c,d,e) 83,232-236 3-phenoxy benzyl-(1ac) 12 and allethronyl-(1ab) chrysanthemates have been synthesized on reaction with peracids (Scheme 103, entries a-e), 12,83,217,232,235 or with hydrogen peroxide in the presence of (i) formamide (Scheme 103, entry f), 233 in a reaction derived from the Payne reaction, 237 or (ii) sodium hydrogenocarbonate catalyzed by manganese sulfate (Scheme 103, entry g). 234,236 Scheme 103.…”

“…Synthesis of oxido-chrysanthemic acid and related esters. 12,83,217,[232][233][234][235][236] The reaction proceeds in all the cases with controlled stereochemistry on the cyclopropane ring but delivers in all the cases checked 12,83,232,235 a mixture of epimeric epoxides at C-4 [for example a 54/46 mixture of(1R,3R,4S)-(16Me) / (1R,3R,4R)-(16Me) (de 8%) on reaction of (1aMe) with meta-chloroperbenzoic acid (m-CPBA, Scheme103, entry c)]. 232 Although most of the reactions have been carried out on alkyl cis/trans-mixtures or trans-chrysanthemates 1aR, it seems that both stereoisomers react equally well at least with m-CPBA and with all the reagents tested except with monoperphthalic acid that has been reported to react poorly on transchrysanthemic acid trans-(1aH) 217 and not at all with its cis-stereoisomer cis-(1aH) probably due to unfavorable steric interactions (Scheme 103, compare entries a,b).…”

“…12,83,217,[232][233][234][235][236] The reaction proceeds in all the cases with controlled stereochemistry on the cyclopropane ring but delivers in all the cases checked 12,83,232,235 a mixture of epimeric epoxides at C-4 [for example a 54/46 mixture of(1R,3R,4S)-(16Me) / (1R,3R,4R)-(16Me) (de 8%) on reaction of (1aMe) with meta-chloroperbenzoic acid (m-CPBA, Scheme103, entry c)]. 232 Although most of the reactions have been carried out on alkyl cis/trans-mixtures or trans-chrysanthemates 1aR, it seems that both stereoisomers react equally well at least with m-CPBA and with all the reagents tested except with monoperphthalic acid that has been reported to react poorly on transchrysanthemic acid trans-(1aH) 217 and not at all with its cis-stereoisomer cis-(1aH) probably due to unfavorable steric interactions (Scheme 103, compare entries a,b). 217 The epoxidation of olefins with peracids, the Prilezhaev reaction, 238 is one of the easiest and most efficient method to produce epoxides from trisubstituted olefins, that are amongst the most reactive olefins; It usually produces stereoselectively epoxides possessing the same stereochemistry as the starting olefins (Scheme 103, entries a-e, Scheme 104, entry a).…”

“…217 The epoxidation of olefins with peracids, the Prilezhaev reaction, 238 is one of the easiest and most efficient method to produce epoxides from trisubstituted olefins, that are amongst the most reactive olefins; It usually produces stereoselectively epoxides possessing the same stereochemistry as the starting olefins (Scheme 103, entries a-e, Scheme 104, entry a). 12,83,217,232,235 Although several peracids are used for such purpose, mchloroperbenzoic acid, proved to be one of the most efficient: it is stable enough to be commercially available and enough reactive due to the presence of the electron-withdrawing chloro substituent on the aromatic ring. It can be easily prepared by reaction of hydrogen peroxide with m-chlorobenzoic acid in the presence of an acid or by reaction of an acid chloride with hydrogen peroxide.…”

Pyrethroid insecticides Chapter IVb. Selected transformations of chrysanthemic acid and its lower esters to Pyrethroid. Use of the Wittig and related reactions

“…Multistep racemization of methyl (1S)-trans-chrysanthemate allowing the access to racemic alkyl cis-and trans-chrysanthemates. 63,185,187 The next racemization process differs from the others since it involves a two steps transformation in which the cleavage of the [Cb-Cd] bond, and the formation of the cyclopropane ring are fully dissociated (Scheme 87).…”