Chiral chloride

The chiral chloride salt is stable for years when kept dry and in the dark, preferentially in a refrigerator at — 15 °C. When heated, the solid salt dehydrates and undergoes racemization.11 In acid solution the A-cis-[Cr(en)2Cl2] + cation aquates to A-cis-[Cr(en)2(H20)Cl]2+ followed by racemization of this complex. In acid solution, Ag+-assisted hydrolysis leads to the A-cis-[Cr(en)2(H20)2]1+ complex.12... 

A different report provided the access to a highly strained tetracyclic [3.6.6.4] ring system containing a fused tetrahydropyran-(3-lactam moiety [83]. The radical precursors 120 were easily accessible via cycloaddition reaction of the appropriate imines with a chiral chloride derived from enantiomerically pure (+)-3-carene. 

Experimental details synthesis of the key chiral chloride intermediate 51 in the synthesis of (-l-)-pericosine A (26) (Scheme 42.16). To a solution of epoxide 50 (12.8 mg, 0.048 mmol) in Et20 (5mL) was added 1-M HCl (0.1 mL, excess) in Et20 at 0°C. After stirring for 1 hour, the solvent was removed in vacuo to give a crude residue that was purified by flash chromatography (silica gel, hexane/EtOAc, 2/1) to afford 51 (12.4 mg, 85%) as colorless crystals. 

Present in citronella and valerian oils, tur penline, ginger, rosemary and spike oils. It is produced artificially by the elimination of hydrogen chloride from bornyl chloride (artifi cial camphor) or from isobornyl chloride, by the dehydrogenation of borneol and isobor-neol and by the action of elhanoic anhydride on bornylamine. Chiral. 

Chiral 2-oxazolidones are useful recyclable auxiliaries for carboxylic acids in highly enantioselective aldol type reactions via the boron enolates derived from N-propionyl-2-oxazolidones (D.A. Evans, 1981). Two reagents exhibiting opposite enantioselectivity ate prepared from (S)-valinol and from (lS,2R)-norephedrine by cyclization with COClj or diethyl carbonate and subsequent lithiation and acylation with propionyl chloride at — 78°C. En-olization with dibutylboryl triflate forms the (Z)-enolates (>99% Z) which react with aldehydes at low temperature. The pure (2S,3R) and (2R,3S) acids or methyl esters are isolated in a 70% yield after mild solvolysis. 

The acyl group of the carboxylic acid acyl chloride or acid anhydride is trans ferred to the oxygen of the alcohol This fact is most clearly evident m the esterification of chiral alcohols where because none of the bonds to the chirality center is broken m the process retention of configuration is observed... 

Stereoselective All lations. Ben2ene is stereoselectively alkylated with chiral 4-valerolactone in the presence of aluminum chloride with 50% net inversion of configuration (32). The stereoselectivity is explained by the coordination of the Lewis acid with the carbonyl oxygen of the lactone, resulting in the typ displacement at the C—O bond. Partial racemi2ation of the substrate (incomplete inversion of configuration) results by internal... 

Chiral diene—iron tricarbonyl complexes were acylated using aluminum chloride to give acylated diene—iron complexes with high enantiomeric purity (>96% ee). For example, /ra/ j -piperjdene—iron tricarbonyl reacted with acyl haUdes under Friedel-Crafts conditions to give l-acyl-l,3-pentadiene—iron tricarbonyl complex without any racemization. These complexes can be converted to a variety of enantiomericaHy pure tertiary alcohols (180). 

The synthesis of optically active epoxy-1,4-naphthoquinones (69) using ben2ylquininium chloride as the chiral catalyst under phase-transfer conditions has been reported (67). 2-Meth5l-l,4-naphthoquinone (R = CH ) (31) yields 70% of levorotatory (37). 2-Cyclohexyl-l,4-naphthoquinone... 

Use ofMethanesulfonyl Chloride (MSC) in the Synthesis of Chiral Compounds, Technical Bulletin A-70-11, Elf Atochem North America, Philadelphia, Pa., 1992. 

The advantages of titanium complexes over other metallic complexes is high selectivity, which can be readily adjusted by proper selection of ligands. Moreover, they are relative iaert to redox processes. The most common synthesis of chiral titanium complexes iavolves displacement of chloride or alkoxide groups on titanium with a chiral ligand, L ... 

Lehn and his coworkers have prepared a number of chiral cryptands based upon the 2,2 -binaphthyl unit " . In a typical preparation, the binaphthyl units are treated with bromoacetic acid to form the phenoxyacetic acid derivatives which are then converted into the corresponding diacyl chlorides (75). Reaction of 15 with l,10-diaza-18-... 

The imidazolidine was prepared from an aldehyde with A,W -dimethyl-l,2-ethylenediamine (benzene, heat, 78% yield) and cleaved with Mel (Et20 H2O, 92% yield). Derivatization is chemoselective for aldehydes. The imidazolidine is stable to BuLi and LDA and to Li/NH3. The diphenylimidazolidine has been prepared analogously and can be cleaved with aqueous HCl." Alternatively, it can be prepared by using thionyl chloride (Pyr, CH2CI2, 0-25°, 7 h, 93% yield). A chiral version using -dimethyl-15,25-diphenyl-1,2-ethylenediamine has... 

With a chiral phenylglycinol nucleophile (Scheme 8.4.17), use of the chloride Zincke salt 6 (cf. Scheme 8.4.16) gave decomposition of the salt back to isoquinoline and 2,4-dinitrochlorobenzene. The desired reaction was enabled by exchanging chloride for the weakly nucleophilic dodecyl sulfate anion. The resulting salt 49 also had improved... 

The chiral bicyclic imidazolidine 74 is deprotonated at the 2 position by s-BuLi and the resulting anion adds to alkyl halides, acid chlorides, chlorofor-mates, phenyl isocyanate, and aldehydes. The use of this compound as a chiral formyl anion equivalent seems to be limited, however, since the diastereoselectiv-ity in the addition to aldehydes is poor and hydrolysis of the products 75 to give aldehydes also produces cyclohexane-1,2-diamine, necessitating isolation of the aldehyde as its 2,4-dinitrophenylhydrazone (96SL1109 98T14255). 

A chiral titanium complex with 3-cinnamoyl-l,3-oxazolidin-2-one was isolated by Jagensen et al. from a mixture of TiCl 2(0-i-Pr)2 with (2R,31 )-2,3-0-isopropyli-dene-l,l,4,4-tetraphenyl-l,2,3,4-butanetetrol, which is an isopropylidene acetal analog of Narasaka s TADDOL [48]. The structure of this complex was determined by X-ray structure analysis. It has the isopropylidene diol and the cinnamoyloxazolidi-none in the equatorial plane, with the two chloride ligands in apical (trans) position as depicted in the structure A, It seems from this structure that a pseudo-axial phenyl group of the chiral ligand seems to block one face of the coordinated cinnamoyloxazolidinone. On the other hand, after an NMR study of the complex in solution, Di Mare et al, and Seebach et al, reported that the above trans di-chloro complex A is a major component in the solution but went on to propose another minor complex B, with the two chlorides cis to each other, as the most reactive intermediate in this chiral titanium-catalyzed reaction [41b, 49], It has not yet been clearly confirmed whether or not the trans and/or the cis complex are real reactive intermediates (Scheme 1.60). 

An X-ray structure of the complex formed between 3-cinnamoyl-l,3-oxazohdin-2-one and a chiral TADDOL-Ti(IV) complex (see Chapters 1 and 6 by Hayashi and Gothelf, respectively) has been characterized [16]. The structure of this complex has the chiral TADDOLate and cinnamoyloxazohdinone ligands coordinated to titanium in the equatorial plane and the two chloride ligands in the axial plane and is similar to A in Fig. 8.8. The chiral discrimination was proposed to be due to... 

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