Zinc alkyl

These facts are perfectly matched with our above-mentioned desired requirements. In addition, alkyl zinc is known to be less basic and deprotonation of ketone-aniline 36 by zinc reagent is highly unlikely. However, one of the issues for this reaction was the requirement for two alkyl groups on the zinc metal since the product ends up as tetramer 61, where the zinc atom still has one alkyl group, recalling that our cyclopropylacetylene (37) is not easy to obtain. 

Zinc alkoxide and aryloxide complexes have been of particular interest as enzyme models and catalysts. Tetrameric alkyl zinc alkoxides are a common structurally characterized motif.81... 

Scheme 13. Synthesis of alkyl zinc complexes with his(pyrazol-l-yl) acetato ligands (47).

The sequential approach is also common in proposals written by synthetic chemists (a multistep synthesis is inherently step by step). Vyvyan (excerpt 13N), for example, proposes a strategy to synthesize a select group of heliannuols (alleo-pathic natural products isolated from the sunflower) in an optically pure form. One approach that he will explore involves enantioselective cross-coupling reactions between an alkyl zinc reagent and an aryl bromide. He begins with experiments that will utilize recently developed catalysts and produce products with known optical rotation data. Subsequent reactions are described that will lead potentially to the desired stereospecific heliannuols A and D. 

Once this process is explored with the model system to assess the level of enantioselectivity, we will then prepare alkyl zinc reagent 48 from 44 using standard methods - - and cross couple 48 to aryl bromide 18 using the appropriate chiral catalysts (Scheme 7). Although the acetonide stereocenter in 48 is somewhat remote from the coupling site, the stereocenter may serve to enhance the stereoselectivity of the cross-coupling process because the two possible products are diastereomers, not simply enantiomers. This reaction will produce 49 from (S)-48 and 30 from (R)-48 that can then be converted to epoxides 31 and 32 using standard methods. Epoxide 31 leads to heliannuol D 4 after base-promoted epoxide cyclization and deprotonation. Similarly, epoxide 32 leads to heliannuol A 1 after acid-promoted cyclization. 

Nakamura and co-workers used /-pr-box ligand 22 stoichiometrically for the addition of alkyl zinc reagents 186a-c to cyclic imines 187a and 187b. This... 

A mandelamide diastereomer catalyses addition of both aryl- and alkyl-zincs to heteroaromatic aldehydes in high yield and ee, giving heterocyclic propargyl alcohols, under otherwise metal-free conditions 228... 

This method is effective for aldehydes bearing a or /1-alkyl substituents and alkyl zincs other than Et2Zn. It is noteworthy that only negligible alkylation of aldehyde (< 2%) is observed under these conditions. The produced amines can be further elaborated to optically enriched acylated amines with high efficiency and without any detectable loss of enantiopurity (Scheme 9.25). 

A field test was conducted to evaluate the valve train wear in a 2.3 L OHC (over-head cam) engine with new technology crankcase lubricants these oils also passed the V-D test (Haris and Zakalka, 1983). Oils formulated with secondary alkyl zinc dithiophosphate (ZDDP) wear inhibitor provided significantly better wear protection than two different primary alkyl ZDDPs. Secondary alkyl ZDDP demonstrated good wear protection at a phosphorus content as low as 0.07 (wt%). 

Alkyl zinc iodides RFG—Zn—I are poor nucleophiles. However, they are turned into good nucleophiles when they are converted into the so-called Knochel cuprates RFG— Cu(CN)ZnHal with solubilized CuCN—that is, CuCN containing LiHal. In the presence of a Lewis acid Knochel cuprates add to aldehydes, provided these are a,/f-unsaturated. With substituted oc,/3-unsaturated aldehydes a 1,2-addition can be observed, as shown in Figure 10.38. With acrolein (an unsubstituted f/./l-u nsaturated aldehyde) or a,/J-unsaturated ketones (Fig. 10.43), however, Knochel cuprates undergo 1,4-additions. 

In a related reaction, addition of organocuprates, alkyl zinc bromide or di-isobutyl aluminium hydride to l-trimethylsilylcyclopropenes occurs regio- and stereo-selecti-vely, eg.12) ... 

Alkyl zinc iodides RFG—Zn—I are poor nucleophiles. However, they are turned into good nucleophiles when they are converted into the so-called Knochel cuprates Rfg—Cu(CN)ZnHal with solubilized CuCN—that is, CuCN containing LiHal. Knochel cuprates add to aldehydes in the presence of Lewis acid, as shown in Figure 8.29. 

A Ni-catalyzed cyclization cross-coupling reaction of iodoalkenes with alkyl zinc halides has been employed for the synthesis of various tetrahydrofuran derivatives <2007AGE-ASAP>. The TiCU-catalyzed anti-Markovnikov hydration of alkynes has been applied to the synthesis of various benzo[3]furans <2007JOC6149>. 

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