Hexamethyldisilazane Sodium

NaHMDS sodium hexamethyldisilazane, sodium bis(trimethylsilyl)amide... 

The generation of ion pairs from NH-unsubstituted tetrazoles has also been performed using sodium salts and sodium hydroxide. Tetrazole alkylation with benzyl chloromethyl ether in tetrahydrofuran (THF) in the presence of sodium hexamethyldisilazane (NaHMDS) has been reported < 1995J(P 1) 1747, 1998SL528>. Regioisomers 240 and 241 formed under these conditions in comparable amounts (Scheme 24) <1998SL528>. 

Z)-l-Iodo-l-alkenes. Reaction of sodium hexamethyldisilazane with the phos-phonium salt 1 in THF generates iodomethylenetriphenylphosphorane, (C6H5)3P=CHI, which converts aldehydes into (Z)-vinyl iodides (15-62 1) in reactions conducted at —78° in THF/HMPT in 61-91% yield.2... 

AD-mix-P 9-BBN Bn Boc Bz BOM CDI m-CPBA CSA Cy DBU DDQ DEAD DIAD DIBAL-H DIPT DME DMF DMAP DMSO EDC HMPA HOBT KHMDS LDA MEM MOM MoOPH NaHMDS NBS NMM NMO Piv PMB Reagent for Sharpless asymmetric dihydroxylation 9-Borabicyclo[3.3.1 ]nonyl Benzyl t-Butoxy carbonyl Benzoyl B enzyloxy methyl Carbonyldiimidazole m-Chloroperoxybenzoic acid Camphorsulfonic acid Cyclohexyl 1,8 -Diazabicy clo[5.4.0] undec-7-ene 2,3 -Dichloro-5,6-dicyano-p-benzoquinone Diethyl azodicarboxylate Diisopropyl azodicarboxylate Diisobutylaluminum hydride Diisopropyl tartrate Dimethoxyethane A,N-Dimethylformamide 4-Dimethylaminopyridine Dimethyl sulfoxide N-(3-Dimethylaminopropyl)-A -ethylcarbodiimide Hexamethylphosphoramide 1 -Hydroxybenzotriazole Potassium hexamethyldisilazane Lithium diisopropylamide Methoxyethoxymethyl Methoxymethyl Oxidodiperoxymolybdenum(pyridine)(hexamethylphophoramide) Sodium hexamethyldisilazane N - Bromosuccinimide A-Methylmorpholine A-Methylmorpholine A-oxide Pivaloyl /j-Methoxybenzyl... 

Table 1. Bromoeyclopropanes from Dibromomethane, Sodium Hexamethyldisilazan-ide and Alkenes in Pentane at 20 °C...

Dimethyl-3-dimethylamino-2//-azirine (X) was reacted (a) with BFs-etherate at -78°C in CH2CI2, (b) with benzamide (Y) in the presence of sodium hexamethyldisilazane in THF at -78°C. After workup, a new heterocylic product (A) was isolated in 49% 5neld (together with 49% of unreacted Y). 

Reactive ylides, in apolar solvents under salt-free conditions, preferentially form olefins with the (Z)-configuration (see Section C.l). To optimize this effect, various techniques have been developed for preparing salt-free ylide solutions [21-25]. The phosphonium salt is deprotonated, for example with sodium amide in THF or liquid ammonia [23], with sodium hexamethyldisilazane in an ether solvent such as THF [21], or with potassium r-butoxide in THF or toluene [22], with the addition of crown ether if appropriate [24]. A particularly elegant application of the salt-free Wittig reaction is the instant-ylide technique [25]. 

Deprotonation with sodium hexamethyldisilazane in tetrahydrofurane followed by treatment with methyliodide yielded the anti-compound 301 in a 95 5 ratio, while the addition of hexamethylphosphoramide (HMPA) to the above enolate broke the chelation and led to syn-compound 302 (ratio 90 10) in the subsequent alkylation. 

The utilization of the Wittig reaction to prepare functionalized alkenes such as Z-vinyl halides has also been demonstrated since the early 1990s (Fig. 2) [12]. The iodoalkyl phosphonium salt is deprotonated with sodium hexamethyldisilazane to yield the ylide that reacts with aldehydes to generate the Z-alkenyl halides in good to excellent selectivity. Not only disubstituted Z-alkenyl halides, but also trisubsti-tuted ones can be prepared using this method, albeit with moderate chemical yields [13]. These products are useful synthons in organic synthesis, especially in cross coupling reactions. 

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