Reaction with Alkyl-or Aryllithium

Organolithium compounds are less reactive than lithium organocuprates. A number of publications deal with the differences observed between the two reagents in the ring-opening reaction of oxiranes. The reaction of 1,3-cyclohexadienemonooxirane with methyllithium is seen in Eq. 277.  

With asymmetrically substituted oxiranes the alkyl group is incorporated here on the more easily approachable side. The action of phenyllithium on chlorooxiranes has been examined. Depending on the structure of the oxirane, the transformations found in Eqs. 278-280 take place these could be of value for preparative purposes. 

By variation of the solvent, not only alkyl-substituted oxiranes but also a,P-unsaturated alcohols can be obtained from halooxiranes (Eq. 281).  

A general method for the preparation of 3,7-substituted allyl alcohols with (Z)-configuration has been developed with alkyllithium. The regioselectivity of the reactions of alkynyllithium and oxiranes ° ° and the effects of the solvent and (Me2N)3PO ° have been investigated with regard to the formation of homo-propargyllic alcohols. The stereochemistry of the process has been studied in the reactions of as- and fra 5-neopentylallyllithium with cyclohexene oxide and fra s-2,3-butene oxide. 

Phenyllithium effects proton abstraction from medium-ring oxiranes (Eq. 282) °  

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Starting with (5)-1 -phenylethyl amine, a chiral sulfonyloxaziridine has been prepared by A,T-sul-fonylation and subsequent formation of an imine with an aromatic aldehyde (best example pentafluorobenzaldehyde). Oxidation leads to a 1 1 mixture of diastereomeric oxaziridines 77 which can be separated by HPLC76. The compounds behave similarly to the chiral camphor-derived sulfonyloxaziridines, as they are able to epoxidize alkenes not containing special functional groups with some enantioselectivity (Section D.4.5.2.1.). Another attractive starting material is cheap commercial saccharin. Reaction with alkyl- or aryllithium compounds leads to addition... 

Reaction with alkyl- or aryllithiums proceeds in two discrete steps addition to give a dihydropyridine 7V-lithio-salt which can then be converted into the substituted aromatic pyridine by oxidation (e.g. by air), disproportionation, or elimination of lithium hydride.The A -lithio-salts can be observed spectroscopically and in some cases isolated as solids. Attack is nearly always at an a-position reaction with 3-substituted-pyridines usually takes place at both available a-positions, but predominantly at C-2. This regioselectivity may be associated with relief of strain when the 2-position rehybridises to sp during addition. 

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