Homo-Peterson Reaction

Reaction of a-silylcarbanions with epoxides has led to observation of the homo-Peterson reaction (equation 134)207. 

The homo-Wittig, homo-Horner, homo-Peterson reaction... 

Silyl-Substituted Carbanions (Homo-Peterson Reaction)... 

This reaction type necessitates, after intermolecular ring opening of the oxirane by a stabilized silyl-substituted carbanion, interaction between oxygen and silicon atoms situated on adjacent carbon atoms, to give substituted cyclopropanes via an intramolecular Spji process. The homo-Peterson reaction is nonstereospecific and occurs at low temperatures. This is in contrast to the cyclopropanation of oxiranes with phosphorous ylides (see Section 1.2.2.1.) or di-ethoxyphosphoryl-substituted carbanions (see Section 1,2.2.2.), which require heating for a long period to accomplish the same transformation. 

Bis(phenylsulfanyl)](trimethylsilyl)methyllithium and trimethylsilyloxirane do not afford a homo-Peterson reaction product, but a cyclopropane 4 a with a shifted phenylsulfanyl group. [Bis(phenylsulfanyl)](trimethylsilyl)methyllithium may be looked on as a carbenoid species which is in equilibrium with carbene and phenylsulfonate. This equilibrium may lie towards the carbanion. On addition of trimethylsilyloxirane, phenylsulfonate is trapped with formation of an alkoxide, which corresponds to the intermediate of a Peterson olefination of formaldehyde, and leads to phenyl vinyl sulfide. This provides a reaction partner for the liberated carbene giving cw-l,2-bis(phenylsulfanyl)-l-trimethylsilylcyclopropane (4a) in a stereospecific [2-1-1]... 

A homo-Peterson process intervened upon 1,4-rearrangement of the alkoxide formed by addition of tris(trimethylsilyl)methyllithium 124 to styrene oxide. The resulting carbanion 125 led mainly to the homo-Peterson product 126, with some of the adduct 127 from addition to a second equivalent of the epoxide. In their report, Fleming and co-workers noted that the homo-Peterson reaction is probably favored in this case by the benzylic positioning of the silyloxy group in 125, and they discussed the parallel between the Peterson olefination and a 1,3-Brook rearrangement process. ... 

In 1989, Schaumann and Friese disclosed a synthesis of cyclopropanes from oxirane and 2-lithio-2-TMS-l,3-dithiane enploy-ing a homo-Peterson reaction (eq 23). Use of thiophenol as the anion stabilizing group led to cyclopropanes via an alternate reaction pathway. 

There have been a few reports on the homo-Peterson reaction, that is the reaction of an a-silyl carbanion with an oxirane to afford the corresponding cyclopropane. The reaction of tris(trimethylsilyl)methyllithium with styrene oxide forms the corresponding cyclopropane 210 (Scheme 2.133) [366]. Appropriate selection of the oxirane is important for this reaction. Both propene oxide and cyclohexene oxide protonate the carbanion, while stUbene oxide is inert towards it. 

Scheme 2.133. Homo-Peterson reaction of tris(trimethylsilyl)methyllithium with styrene oxide.

Carbanions 211 with arylthio or alkylthio substituents at the attacking carbon are used for homo-Peterson reactions (Scheme 2.134) [367]. The intermediary alkoxide 212 can transfer a silyl group from the carbon to oxygen, and subsequent attack of the carbanion 213 gives the cyclopropanes 214. 

R = Ph, Me R = SiMes, SMe R = Ph, SiMes Scheme 2.134. Homo-Peterson reaction of a-silyl alkyllithiums with epoxides. 

The spirocompounds 34 (M = Ti or Zr) have been prepared . Studies of the thermolysis of pentacoordinate 1,2-oxasiletanides 35, potential intermediates in both the Peterson reaction and the homo-Brook rearrangement of p-hydroxyalkylsilanes with bases, in the presence of a proton source afforded the olefin, RCH=C(CF3)2 and/or the alcohol, (CF3)2CHOH <99CL1139>. 

Intermediacy of pentacoordinate oxasiletanides in the Peterson olefination reaction has been discussed <2002CSR195, B-2004MI18>. Products of thermolysis of 1,2-oxasiletanides indicate that they are the intermediates of both Peterson and homo-Brook reactions <1999CL1139, 2003BCJ471>. 

Naganuma, K., Kawashima, T., Okazaki, R. Control factors of two reaction modes of pentacoordinate 1,2-oxasiletanides, the Peterson reaction and homo-Brook rearrangement. Chem. Lett 1999, 1139-1140. 

Homo-Peterson Alkenation. Styrene oxide reacts with lithio-phenylthiobis(trimethylsilyl)methane to afford cyclopropane-containing products (eq 6)7 This reaction is limited, due to the complexity of its mechanism the alkenation reagent must serve to generate both alkenic and carbenic species. For this reason, only styrene oxide and trimethylsilyloxirane undergo this transformation. 

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