Oxiranyllithiums

This usually generates a carbene (Section 5.05.3.2.2), but the oxirane (61) is deprotonated by butyllithium to the versatile oxiranyllithium (62 Scheme 59) (76JA4646). 

Oxazolinyl-oxiranyllithiums (357) prepared from optically pure oxazolinyloxi-ranes react with nitrones diastereo and enantioselectively to give almost optically pure diazadispiroundecanes (358). These are appropriate candidates for the conversion to a-epoxy-P-amino acids (360) in view of the lability of the N-O bond of the isoxazolidinones (359) (Scheme 2.156) (590-596). 

The reaction of sulfinyloxirane 130 with n-C4H9Li takes place at the sulfinyl group to afford the desulfinated epoxide 133 in good yield. This reaction proceeds at — 100°C with concomitant formation of phenyl n-butyl sulfoxide 132. Thus, oxiranyllithium 131 picks up the acidic proton of the in situ formed 132 to generate the reduce epoxide 133 (equation 46) . 

In the case of medium-size cyclic oxiranes, in the presence of diamine ligands, the decomposition of the oxiranyllithium intermediate can be prevented at low temperature and the lithium species can be trapped by various electrophiles (Scheme 52). The use of (—)-sparteine 112 has led to the corresponding functionalized oxiranes in good ee s. 

Capriati, V. Florio, S. Luisi, R. Russo, V. Sal-omone, A. Oxiranyllithium based synthesis of... 

Computational methods have been used to determine the structure, bonding, and aggregation states of oxiranyllithium in the gas phase and in THF solution, at 200 and 298 K.6 Oxiranyllithium was found to exist predominantly as the tetramer in the gas phase, whereas the dimer was the dominant species in THF solution. 

Oxiranyllithium reagents. Epoxides stabilized by a silyl group can be lithiated at the activated position (7, 45-46), but lithiation of nonstabilized epoxides results... 

Reaction of DMSB with triphenylsilyl-substituted oxiranyllithium leads to the formation of an olefinic silanol via sequential (1) coordination to the silicon, (2) Si-C bond migration, and (3) Peterson-type Si-O elimination to furnish the alkene. A pentacoordinate siliconate intermediate is presumably involved in this transformation. Therefore, it was reasonable to expect that addition of a nucleophile (methyllithium or lithium t>-propoxide) to an oxiranyl-substi-tuted SCB, which could generate a similar intermediate, would induce the C-Si bond migration to form the same silacyclopentane. Indeed, this alternative order of addition sequence provides the corresponding silanol with better efficiency (84% yield vs. 44%, Scheme 36). 

Just as cyclopropyllithiums and aziridinyllithiums are highly configurationally stable, it is to be expected that lithiated oxiranes (those that are chemically stable44) also maintain their configuration.45 47 Townsend made use of oxiranyllithium 93 (which can be assumed to have configurational stability) in the synthesis of (+)-cerulenin 94 48... 

Silacyclobutanes as well as silacyclopropanes undergo aldehyde insertion under catalysis by /-BuOK (Equation (77)).292 The reaction of silacyclobutanes with lithium carbenoids such as dihalomethyllithium and oxiranyllithium gives 2-substituted silacyclopentanes (Equation (78)). Treatment of l-(l-iodoalkyl)- and 1-oxiranyl-silacyclobutanes with a stoichiometric amount of an alkali alkoxide leads to silacyclopentanes by anionic 1,2-shift of the ring carbon adjacent to silicon. These ring-expansion reactions proceed probably via a pentacoordinate silane intermediate. 

Enantiopure sulfinyl and sulfonyl oxiranes are versatile synthetic intermediates. Mori and colleagues reported that oxiranyllithium compounds, generated from... 

Handling, Storage, and Precautions the oxiranyllithium is very unstable, even at —100 °C under argon, and should be reacted with electrophiles immediately. The reagent is also conforma-tionally unstable and slowly isomerizes to the trans-isomer when addition of an electrophile is delayed (about 5% isomerization after 20 min at -100 °C). Elevated temperatures (>—78 °C) cause rapid decomposition. - ... 

Reaction of the oxiranyllithium with aldehydes is also carried out by an in situ trapping method at very low temperatures in order to avoid decomposition of the reagent. Its applicability to a complex situation has been demonstrated in a synthesis of hemi-... 

While alkylation of sulfonyl-stabilized oxiranyllithiums with primary alkyl triflates proceeds in high yield, the reaction towards epoxides is relatively slow ( 2 h) and the decomposition of oxiranyllithium is marked, such that it decreases the yield, especially in the case of a Z-isomer (eq 7 and 8). Addition of boron trifluoride diethyl etherate promotes this epoxide-epoxide coupling reaction. One of the diastereoisomers of eq 8 has been elaborated via 5-endo cyclization into a marine tetrahydrofuran isolated from a brown alga. ... 

Related Reagents. Optically active trisubstituted sulfonyl-stabilized oxiranyllithiums can be generated by deprotonation of the corresponding epoxy sulfones (eq 9). Due to the diminished reactivity of the reagents by steric hindrance, the reaction with triflates requires HMPA to obtain a high yield of product (eq 10). ... 

The reaction of 191a with oxiranyllithiums as hthium carbenoids gives 2-(l-sil-... 

Nagald A, Taldzawa E, Yoshida J (2010) Generation and reactions of oxiranyllithiums by use of a flow microreactor system. Chem Eur J 16 14149-14158... 

An overview of oxiranyllithiums as chiral synthons for asymmetric synthesis discussed the generation of a-lithiated oxirane derivatives by various synthetic methods." The mechanism and stereochemical features in asymmetric deprotonafion... 

When generated under the aforementioned conditions, oxiranyllithiums 2a have proved to be (1) excellent nucleophiles and (2) configurationally stable on the timescale of their reactions. Thus, starting from optically active... 

Table 1 Enantiomerization barrier and activation parameters for representative oxiranyllithiums 8—14...

Figure 1 (a) Barriers to inversion of oxiranyllithium 10/ligand complexes in hexane/ TMEDA at 195 K (b) enantiomerization barrier of oxazolinyl oxiranyllithium 17 in THF/EtjO at 143 K. 

Reaction of Sulfonyl-stahilized Oxiranyllithiums. Reaction of sulfonyTstablllzed oxiranyllithiums with primary alkyl halides gives acceptable yields of products. More reactive alkyl triflates give generally better yields but, due to the instability of oxiranyl-hthlums, yields are often not reproducible when electrophiles... 

Reiterative application of this protocol has allowed the stere-ocontrolled construction of polytetrahydropyrans and polycyclic ethers containing six- and seven-membered rings (eq 5). Reaction of the oxiranyllithium with aldehydes is also carried out by an in situ trapping method at very low temperatures in order to avoid decomposition of the reagent. Its applicability to a complex situation has been demonstrated in a synthesis of hemibrevetoxin B (eq 6). It is noteworthy that deprotonation of 1 by n-BuLi is much faster than butyl addition to the aldehyde. 

Asymmetric epoxides (64) and alcohols (65) have been synthesized from sulflny-loxiranes (63) via oxiranyllithiums and oxiranyl Grignard reagents which bear a carbanion-destabilizing alkyl group (Scheme 10). ... 

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