Schwartz s reagent

A valuable feature of the Nin/Crn-mediated Nozaki-Takai-Hiyama-Kishi coupling of vinyl iodides and aldehydes is that the stereochemistry of the vinyl iodide partner is reflected in the allylic alcohol coupling product, at least when disubstituted or trans tri-substituted vinyl iodides are employed.68 It is, therefore, imperative that the trans vinyl iodide stereochemistry in 159 be rigorously defined. Of the various ways in which this objective could be achieved, a regioselective syn addition of the Zr-H bond of Schwartz s reagent (Cp2ZrHCl) to the alkyne function in 165, followed by exposure of the resulting vinylzirconium species to iodine, seemed to constitute a distinctly direct solution to this important problem. Alkyne 165 could conceivably be derived in short order from compound 166, the projected product of an asymmetric crotylboration of achiral aldehyde 168. 

Schlosser s super base 615 f. Schmidt trichloroacetimidate glyco-sidation 528,531,537,556 Schwartz s reagent 606, 616 scopadulcic acid A 571 scopadulcic acid diterpenes 569 secocorrin 100, 122, 126 f., 130... 

In this method, one alkyne is treated with Schwartz s reagent (see 15-17) to produce a vinylic zirconium intermediate. Addition of MeLi or MeMgBr, followed by the second alkyne, gives another intermediate, which, when treated with aqueous acid, gives the diene in moderate-to-good yields. The stereoisomer shown is the one formed in usually close to 100% purity. If the second intermediate is treated with I2 instead of aqueous acid, the 1,4-diiodo-1,3-diene is obtained instead, in comparable yield and isomeric purity. This reaction can also be done intramolecularly Diynes 56 can be cyclized to ( , E) exocychc dienes 57 by treatment with a zirconium complex. 

Scheme 8-4 Synthesis of zirconocene hydride Cp2Zr(H)OTf alternative to the Schwartz s reagent, ...

The chemoselectivity of Schwartz s reagent (1) toward alkynes, alkenes, nitriles, and carbonyl groups, and thus its general functional group compatibility, can be modulated. However, it is important to keep in mind that the presence of functional groups may have regiochemical consequences on the hydrozirconation reaction. 

As described in the previous section for unsaturated functional groups, Schwartz s reagent (1) and most zirconocene(IV) hydrides readily deprotonate acidic moieties [183, 218]. 

Cp(PMe3)2RuC=CH and the corresponding vinyl compound react with 1 to give the expected hydrozirconated complexes [225, 226]. Hydrozirconation reactions were also observed with the vinyl and acetylenic ferrocenyl complexes [227]. In marked contrast, the iron complex Cp (dppe)Fe-C=CH reacts anomalously with Schwartz s reagent to form acetylide Cj-bridged heterodinuclear complexes (Scheme 8-31) [228]. 

Schwartz s reagent (1) is an excellent catalyst for pinacolborane hydroboration of alkynes (Scheme 8-32) [234, 235]. 

Since the initial reports of Schwartz s reagent ([Cp2Zr(H)Cl]n, 1) over 30 years ago there has been explosive growth of zirconocene chemistry. Hydrozirconation is an efficient method of hydrometalation because of (i) the mild nature of the conditions involved, (ii) the excellent regio- and stereo-chemical control of hydrozirconation, (iii) the one-pot nature of the procedure, and (iv) the price of Zr, which is one of the... 

Schwartz s Reagent Bis(cyclopentadienyl)zirconium chloride hydride Zirconium, chlorodi-B-cyclopentadienylhydro- (8) Zirconium, chlorobis(ii5-2,4-cyclopentadien-1-yl)hydro- (9) (37342-97-5)... 

Stephen L. Buchwald, Susan J. LaMaire, Ralph B. Nielsen, Brett T. Watson, and Susan M. King 77 SCHWARTZ S REAGENT... 

Methylene chloride is distilled from calcium hydride under argon at atmospheric pressure immediately before use. It is important to keep the methylene chloride wash in contact with the Schwartz s Reagent for a maximum period of 10 min use of a frit filter is essential. 

Schwartz s Reagent is an air, moisture, and moderately light sensitive compound that should be dried in the dark, and protected from moisture and light during storage. 

A dimetal species, obtained by treatment of vinylzinc with Schwartz s reagent, leads to a very effective alkylidenation reaction as shown in Scheme 1843. 

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