Lithium, organo-, reagents

All that has been said in this section applies with equal force to the use of organo-lithium reagents in the synthesis of alcohols. Grignard reagents are one source of nucleophilic carbon organolithium reagents are another. Both have substantial carbanionic char acter in their- car bon-metal bonds and undergo the same kind of reaction with aldehydes and ketones. 

Isoquinoline 53 was also used as a substrate for the addition of organo-lithium reagents by Alexakis and Amiot (Scheme 13) [13]. While remaining quite modest, the best enantioselectivities (48%) were still reached with sparteine after quenching with methyl chloroformate. However, a mixture of mono- and bisacylated products 54 and 55 were obtained in all cases and the use of a catalytic amount of sparteine lowered the selectivity of the adducts. 

Several examples of intramolecular additions to carbonyl groups by organo-lithium reagents generated by halogen-metal exchange have been reported, such as the two examples shown below. What relative reactivity relationships must hold in order for such procedures to succeed ... 

A different approach to unsymmetrical diorganyl tellurides, in which an electrophilic tellurium species is used, involves the nucleophilic attack of organomagnesium or organo-lithium reagents to diorganyl ditellurides. 

Scheme 7.4 illustrates some of the important synthetic reactions in which organo-lithium reagents act as nucleophiles. In addition to this type of reactivity, the lithium reagents have enormous importance in synthesis as bases and as lithiating reagents. The commerically available methyl, w-butyl, 5-butyl, and /-butyl reagents are used most frequently in this context. 

The mixed acetal groups are stable to both organo-lithium reagents and living lithium polymers. Such initiators are preparable in high yields (84—92%) and are soluble in diethyl ether or benzene and insoluble... 

The most widely used method for the preparation of organometallic compounds of the heavier alkali metals is from the corresponding organo-lithium reagent and an alkoxide. 

A Grignard or organo-lithium reagent would attack at the less hindered end of the epoxide and the Grignard route gives the alcohol 53. In chapter 12 we shall see that this reaction is stereospecific. 

The organo-lithium reagent can be made by exchange of Li for a halide or by deprotonation. With di-iodide 24, one iodine may be exchanged with one equivalent of BuLi and the aldehyde 25 is the product.6 The aromatic heterocycle isothiazole 26 has its most acidic hydrogen (marked) next to sulfur and it gives one aldehyde 27 in good yield.7... 

Wittig-type olefinations can also be performed using selenoaldehydes. Phosphorus ylides initially attack the carbon atom of the selenocarbonyl functionality.405 Aromatic selenoketones undergo reductive dimerization with organo-lithium reagents probably via an electron transfer mechanism.406 Also the addition of organolithium reagents takes... 

Lack of conjugation leads to increased reactivity, and N-acyl aziridines are useful in synthesis because they react with organo-lithium reagents only once to give ketones. No further reactions of the product ketone occur because the N-acyl aziridine is reactive enough to compete with it for the organolithium reagent. 

Reaction with l-chloro-2-methylcyclohexene (1). This vinyl halide reacts with phenyllithium (5 equiv.) to give the bicyclo[4.1.0]heptane (2) in 90% yield. The paper presents evidence for the intermediacy of the cyclopropene a. Other organo-lithium reagents react in the same way, but yields are lower, 47% in the case of CHjLi. 

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