Adamantyl lithium

Bridgehead adamantyl carbanions have been found to be quite elusive. Attempts to generate bridgehead organometallic derivatives of adamantane frequently result instead in the preparation of 1,1-biadamantane 318> 319). 1-Adamantyl lithium may be obtained, however, by the exchange reaction illustrated in Eq. (81). 

In a very interesting report of Molle and Bauer [7] using adamantyl halides and the hindered ketones hexamethylacetone and adamantanone, they observed no alcohol products when the hindered ketones were mixed with preformed adamantyl lithium at low temperature ( —20 C) in diethyl ether. However, when the ketones and halide were mixed with lithium powder under the same low-temperature conditions, substantial yields of the expected carbinols were isolated. They postulated a surface-mediated radical ion or radical pair reaction with the ketone or the ketyl radical. The reaction of a ketyl with the halide was ruled out because earlier researchers [4] had shown that no carbinol was obtained from the reaction of an alkyl halide and benzophenone ketyl. The authors also did not find any carbinol product when the ketyl of adamantanone was reacted with adamantyl halide. By extending their studies to other homologues of adamantane, the authors concluded that the stability of the cagelike radical species determined the extent to which the radical pathway is favored over the organometallic pathway. 

Lithium aluminum hydride reduction of 31 in the presence of benzylamine affords a 70% yield of l-benzylamino-2-oxaadamantane.154 This approach is patented as a general method for the preparation of N-substituted 2-oxa-adamantyl-l-amines.155 Transannular cyclization of 31 or 35 in the presence... 

Monomeric carbene complexes with 1 1 stoichiometry have now been isolated from the reaction of 4 (R = Bu, adamantyl or 2,4,6-trimethylphenyl R = H) with lithium l,2,4-tris(trimethylsilyl)cyclo-pentadienide (72). The crystal structure of one such complex (R = Bu) revealed that there is a single cr-interaction between the lithium and the carbene center (Li-C(carbene) 1.90 A) with the cyclopentadienyl ring coordinated in an if-fashion to the lithium center. A novel hyper-valent antimonide complex has also been reported (73). Thus, the nucleophilic addition of 4 (R = Mes R = Cl) to Sb(CF3)3 resulted in the isolation of the 1 1 complex with a pseudo-trigonal bipyramidal geometry at the antimony center. 

E2, 309, 382, 388 aus Phenyl-lithium und Phosphorsaure-chlorid-dipiperidid XII/1, 372 aus Phenyl-magnesiumbromid und Phos-phorsaure-chlorid-diethylester XII/1,372 Thorium-Salz XII/1, 384 Benzol- -(l-adamantyl-amid)-chlorid El, 596 Benzol- -alky (aryl)ester-chlorid... 

Adamantyl)thiacalix[4]arene was synthesized either by condensation of p- 1 -adamantyl)-phenol with sulfur in the presence of base or alkylation of p-//-thiacalix[4]arene with adamantanol in F3CCO2H <02TL5153>. A new macrotricyclic ligand with an N4S2 donor set has been synthesized from cyclam it was shown to encapsulate lithium and transition metal ions <02CC170>. 

E -Enolates often react with lower stereoselectivity than those of the corresponding Z-enolates. A classic example to illustrate this point is a study carried out by Heathcock et al.6 (Scheme 2.IV). When the carbonyl compounds 1 were deprotonated with lithium diisopropylamide (LDA) and the resulting enolates were subsequently treated with benzaldehyde at -72° C, the aldol products desired (2) were obtained in 83 to 99% yield. The Z-enolates derived from t -butyl and 1-adamantyl ethyl ketones afforded syn -products in excellent levels of diastereoselectivity. The fact that the syn/anti ratios directly reflect the isomeric purity of the reacting enolates hints that the Z-enolates in these cases undergo aldol reaction through a chairlike six-membered transition state (Scheme 2.III,... 

Cavell also reported alkyl derivatives. Tetrabenzyl zirconium was found to react separately with one molar equivalent of two parent methanes to afford complexes 135 and 136 in excellent yields.66 The 13C NMR chemical shifts of the methandiide centres in 135 (Ad = adamantyl) and 136 of 82.8 and 84.4 ppm are clearly different from the dichloride congeners and reflect the substitution of the chlorides by alkyls. The corresponding hafnium dialkyl 137 was also prepared from 133 and neopentyl lithium and the methanide resonance for this complex appeared at 71.6 ppm in its 13C NMR spectrum.63 Noteably, these alkyls displayed far greater stability than their homoleptic tetraalkyl cousins. 

The interaction of [MN(SiMe3)2] (M = Li, Na, K) and LiTMP with carbenes (1) (R = i-Pr, R = Me), (3) (R = i-Pr) and (4) (R = Me) in solution was also reported. Evidence of complexation of these carbenes with the Li, Na, and K species in solution was given by the NMR shifts for the relevant carbene center. Recently, the reaction of carbene (1) with lithium l,2,4-tris(trimethylsilyl)cyclopentadienide was reported to result in monomeric carbene complexes with 1 1 stoichiometry (R = H R = f-Bu (6), adamantyl (7), or 2,4,6-trimethylphenyl(8)). The crystal structure of (6) showed that the cyclopentadienyl ring is coordinated in an -fashion to the lithium center (see Alkali Metals Organometallic Chemistry) and there is a single a-interaction present between the lithium and the carbene center (Li-C(carbene)... 

Alkyl but-3-en-l-yn-l-yl tellurium and lithium in liquid ammonia form lithium al-kanetellurolates. The tellurium-ethenyl bond is broken in this reactionh When 1-adamantyl phenyl tellurium was treated with sodium in liquid ammonia, the Te-adamantyl bond is preferentially cleaved, although the Te-phenyl bond is also attacked. The ratio of the fragmentation rates is approximately 13. ... 

Based on the elimination reaction, Pericas and coauthors" have developed a method for the synthesis of acetylenic ethers, derived from tertiary alcohols with a bulky alkyl group such as r -butyl and adamantyl. The key step in this synthesis is the dehydrobromination of l-bromo-2-alkoxyethylene 67 with sodium amide in ammonia or lithium diisopropylamide in a hexane-THF solution (equation 39)". ... 

However, little success was met in the one-step synthesis of l-(2-adamantyl)-2-methyl-2-phenyl-l-ethanol from 2-chloro-2-phenylpropane, adamantanone and lithium in tetrahydrofuran [36]. But when this reaction was run in the presence of a catalytic amount (1-3 mol%) of the aromatic electron-transfer agent 4,4 -di-tm-butylbiphenyl (DBB), the desired tertiary alcohol was obtained in 67% yield ... 

Secondary alkyl bromides are sufficiently reactive under these conditions, but primary alkyl bromides are usually inert and much better results are obtained by using highly activated Rieke-zinc. Thus, the reduction of zinc chloride with lithium naphthalenide, freshly prepared from finely cut lithium and naphthalene in THF, produces within 1.5 h highly reactive zinc (Rieke-zinc). This form of zinc readily reacts with secondary and tertiary alkyl bromides. Adamantyl bromide (217) was converted into the corresponding organozinc reagent 218. Its reaction with cyclohexenone in the presence of BF3 OEt2 and TMSCl afforded the 1,4-addition product 219 in 54% yield (Scheme 2-87). 

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