LDA-HMPA

Double deprotonation/alkylation of (/ )-4-phenyl-3-oxazolidineacetonitrile with LDA/HMPA and epibromohydrin or triflylmethyloxirane afforded the cyclopropyl derivative with a diastereomeric ratio of 44 37 12 7, which was independent of the reaction conditions and the nature of the electrophile70. Since separation of the main isomers by flash chromatography (silica gel, ethyl acetate/hexane 40 60) was possible, optically pure 1 -aminocyclopropanecarb-oxylic acids (methanohomoserines) were obtained after further transformations. 

The preceding results and Ashby s observation (81JOC2429) that LDA acts as the single-electron donor towards aromatic hydrocarbons, stimulated Newkome (82JOC599) to study the reaction of pyridine with LDA (HMPA at 0°C) (Scheme 149). The products of this reaction, 2,4 - (77) and 4,4 - (494) bipyridines, obtained in the ratio 1 8, were rationalized as being formed from a pyridine radical-anion 493. In support of this proposal, complex ESR signals corresponding to both pyridine radical-anion and the diisopropylamino radical were observed under these conditions. 

Elaboration of 2-isoxazolines via their 4-endo-anions has been studied as a method to synthesize y-amino alcohols (78TL3129,3133,81AG(E)601,603). When the 5-methyl-3-phenyl-2-isoxazoline (527) was deprotonated with LDA/HMPA and methylated with methyl iodide, the tra 5-4,5-substituted isoxazoline (528) was formed predominantly (trans-.cis = 12 1). Reduction of this isoxazoline with lithium aluminum hydride proceeded with steric approach control to provide a diastereomeric mixture of y-amino alcohols (529, 530 Scheme 116). The 5-substituent was found to exhibit a greater steric influence on this reaction than the 4-substituent. 

Scheme 1. Key a) alkaline HOOH, THF b) NaSPh, THF c) m-CPBA, CH2CI2, -78 °C d) 2 LDA, HMPA or DMTP, THF, -35 °C then 2-(2-bromoethyl)-2,5,5-trimethyl-1,3-dioxane e) AI(Hg) amalgam, wet THF f) p-CH3PhS02NHNH2, neat, 1 mm Hg g) 4 BuLi, TMEDA, 0 °C then DMF h) DIBAH, Et20, -78 °C then TMSCI, pyridine, CH2CI2 i) t-BuLi, THF, -30 °C then HOAc, -78 °C j) propionic anhydride, DMAP, pyridine, CH2CI2.

Triphenylstannyl group migration also occurs on treatment of ethoxy carbene complexes of the type Cp(CO)2 PhC(OEt) MSnPh3 (M = Mo or W) with LDA/HMPA, with formation of carbyne complexes [( 5-Ph3SnC5H4)(CO)2CPh)], after treatment with PhC(0)Cl405. 

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