Organometallic Derivatives of Epoxides

Abstract

β‐Metalated alkoxides are useful synthetic intermediates. The hitherto difficultly accessible species are formed upon reaction of epoxides with alkalimetal or magnesium salts of naphthalene or biphenyl radical anions. In unsymmetrically substituted epoxides a pronounced regioselectivity of the ring opening is found, the orientation of which depends upon the nature of the substituents.

Studies culminating in the total synthesis and determination of the absolute configuration of (−)-saudin

“…Preliminary studies of the reduction and concomitant trapping of epoxy ketone 5 with electrophiles established that the usual one electron reductants such as Li/NH 3 , 16 Li napthalenide 17 and Li di- tert -butylbiphenylide 18 were too basic and/or nucleophilic, resulting in either degradation of 5 or reduction/elimination back to the enone 19 .…”

Benzylic Organometals via Reductive Metalation Procedures

“…Although requiring a sub-zero reaction temperature, metalation of methyl ether 40 shows distinct advantages, as it does not require ultrasound irradiation, nor the employment of Barbier-type reaction conditions, nor the presence of a high excess of the electrophilic reagent, and does not lead to the formation of Wurtz-type by products. The mildness and efficiency of the reductive metalation of benzyl alkyl ethers is further exemplified by its successful application to the synthesis of -ferrocenyllithium reagents (47), a class of organometals that react with complete retention of configuration with various electrophiles (Scheme 17) [43].…”

“…Reductive metalation of phenyloxirane (49) was realized at low temperature either in the presence of a stoichiometric amount of LiN or of potassium biphenylide (KB), followed by trapping of the resulting organometal (50) with an electrophile [47]. At variance with this result, the reductive lithiation of cis-or trans-2,3-diphenyloxirane (51 and 52) was run under Barbier-type reaction conditions with an excess of the metal and a catalytic amount of DTBB, leading to the formation of the same product with the same stereochemistry independently from the starting material.…”

Chemical Methods for Ether‐Bond Cleavage by Electron‐Transfer Reagents

“…On the other hand, if R is an electron acceptor (Ph, CO 2 C 2 H 5 , [13] CHϭCH 2 , [62] CϵCH [64] ) then the electron is transferred into the antibonding π*-orbital of the substituent and the ring opening occurs in the α-position. This indicates a stabilising effect of the substituent even during the formation of the carbanion.…”

“…[67,68] In unsymmetrical oxetanes the direction of opening is analogous to that observed in the reduction of oxiranes. [13] γ-Lithioalkoxides can provide 2-substituted tetrahydrofurans upon trapping with aldehydes and ketones followed by acid cyclisation of the resulting 1,4-diols; the cuprates of these dianions undergo conjugate addition and nucleophilic substitution reactions. This regiochemistry in the case of oxiranes can be explained by the greater stability of the more-substituted alkoxide, which outweighs the lower stability of the less-substituted radical that is formed by the rupture of the intermediate oxirane radical anion.…”