Alkenyllithium

The organoborate intermediates can also be generated from alkenylboronic esters and alkyllithium or Grignard reagents, or from ttialkylboranes and alkenyllithium compounds. Conjugated symmetrical and unsymmetrical diynes (289—291), stereochemically pure 1,3-dienes (292,293), and 1,3-enynes (294) including functionali2ed systems can be prepared (289,295). 

Organoantimony Compounds with Five Sb—C Bonds. A number of pentaalkyl- and pentaalkenylantimony compounds have been prepared from tetraalkyl- or tetraalkenylstibonium hahdes and alkyl or alkenyllithium or Grignard reagents, for example ... 

Unsubstituted or alkyl-substituted 2-alkenyllithium, -sodium and -potassium derivatives are of little value in stereoselective carbonyl addition reactions. In general, these reagents exhibit high... 

Hetero-substituted 2-alkenyllithium compounds, however, show useful levels of regio- and stereoselectivity in reactions with aldehydes, in particular if the cation is held at one terminus of the allylie system by electron-withdrawing or chelating groups. 

Alkenyllithium derivatives, carrying carbanion-stabilizing substituents, which facilitate the formation of solvent-separated ion pairs, can also exhibit preparatively useful configurational stability in respect to the double bond of the precursor. 

I-(Diisopropylaminocarbonyloxy)-2-alkenyllithium-TMEDA Complexes (Enantiomerically Enriched or Racemic) General Procedure19,6S. 

The stannanes (-)-ent-12 and ( + )-ent- 3 (R = CH3) are obtained with >80% ee from the alkenyllithium (-)-sparteine complex105,107a (Section 1.3.3.3.1.1.). Hence, their titanium(IV) chloride mediated carbonyl additions are accompanied by chirality transfer and enantioface selection of opposite sense. This was demonstrated for the reaction with (5)-2-benzyloxy-propanal107b the d.r. (88 12) roughly reflects the enantiomeric composition of the stannanes. 

As mentioned above, 1-alkenyl aryl sulphoxides can effectively be a-lithiated by treatment with a slight excess of LDA in THF at — 78°. The 1-(arylsulphinyl)alkenyllithium reagents 331 so generated react cleanly and rapidly with a variety of electrophiles to give 1-substituted 1-alkenyl sulphoxides 332 in high yields (equation 191). 

Arylsulphenyl halides, reactions of 282 Arylsulphenylpiperidines 623 Arylsulphinic acids, reactions of 283 Arylsulphinylalkenes 625 (Arylsulphinyl)alkenyllithium reagents 312 2-Arylsulphinyl-a-arylalkanols, synthesis of 252... 

As with organomagnesium reagents, there is usually loss of stereochemical integrity at the site of reaction during the preparation of alkyllithium compounds.25 Alkenyllithium reagents can usually be prepared with retention of configuration of the double bond.26,27... 

Alkenyllithium compounds are intermediates in the Shapiro reaction, which is discussed in Section 5.7.2. The reaction can be run in such a way that the organolithium compound is generated in high yield and subsequently allowed to react with a variety of electrophiles.64 This method provides a route to vinyllithium compounds starting from a ketone. 

Alkenyllithium reagents can be alkylated in good yields by alkyl iodides and bromides.79... 

Similarly, alkenyllithium reagents add to dimethyl boronate to give adducts that decompose to Z-alkenes on treatment with iodine.27... 

A review entitled a-heteroatom-substituted 1-alkenyllithium regents carbanions and carbenoids for C-C bond formation has addressed the methods of generation of such species, illustrated the carbenoid reactivity of a-lithiated vinyl halides and vinyl ethers, and emphasized the synthetic potential of the carbanion species in asymmetric synthesis of a-hydroxy- and a-amino-carbonyl compounds. ... 

Being less basic than the saturated analogs, vinyllithium as all other acyclic or cyclic 1-alkenyllithiums can be prepared from iodo or bromo and sometimes even chloro precursors using butyllithium or fert-butyUithium (Tables 12 and 13). Hetero-substituents such as dialkylamino, alkoxy and silyloxy groups or halogen atoms again accelerate the exchange process considerably (Table 14). This holds for 0-lithiated hydroxy or carboxy functions as well (Table 15). 

If the alkenyllithium 43 is used as organolithium compound with 39, siloxyallyllithium reagents 44 are formed ". As example, the isomerization of the silyl(allyl)alkoxides 44 gives the corresponding lithio-(Z)-silyl enol ethers 45 which react with various electrophiles to give 46 (equation 17) . ... 

The Shapiro reaction occurs when a tosylhydrazone 86, easily prepared from a ketone and tosylhydrazine, is treated with 2 equivalents of an ethereal solution of n-butyllithium 87, resulting first in the removal of the N—H proton to give the anion 88 and then of a one proton from the less-substituted a position to give the dianion 89. Elimination of lithium p-toluenesulfinate in the rate-limiting step gives the lithium aUtenyldiazenide 90, which suffers loss of nitrogen to afford the alkenyllithium 91 (equation 31) ° . ... 

An interesting chain elongation of 4-oxo-l-tributylstannylbutyl carbamate 83 by ethynyl A,A-diisopropyl carbamate (82) to the dicarbamate 84 and the subsequent intramolecular carbolithiation to form the alkenyllithium 86 has been reported very recently (equation 18). 86 was trapped by electrophiles to yield—as expected—both epimers 87 and 88 in essentially equal amounts. From an X-ray analysis of a derivative, the shown absolute configuration and the ( )-stereochemistiy at the double bond was concluded. Thus, the attack at the triple bond here took place in the anti fashion, which is quite unusual. We suggest that a lithium cation in 85, captured by the second carbamoyl group, catalyses the anti addition. ... 

Alkenyllithium and subshtuted alkyllithium reagents can be prepared from sulfides.25 26 The method can also be applied to unsubstituted alkyllithium reagents, although in this case there is no special advantage over the conventional procedure. 

Based on these investigations, stereochemically defined alkenyllithium is treated with stereochemically undefined crotylzinc to give the adduct diastereoselectively (equation 16)26. Many types of stereoselective reactions will be shown in Section . 

They also showed that the gem-dimetal species from allylzinc and alkenyllithium lead to selective reactions with electrophiles as shown in Scheme 201 ,4 . 

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