MeMgBr. addition with

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. 

The lipase-catalyzed resolution of (2/ , 35 )-3-methyl-3-phenyl-2-aziridine-methanol ( )-H by using the low-temperature method gave synthetically useful (2/ ,35 )-ll and its acetate (2S, iR)- a with (25 )-selectivity E = 55 at —40°C), while a similar reaction of (2/ , 3f )-3-methyl-3-phenyl-2-aziridinemethanol ( )-12 gave (25,35 )-12 and its acetate (2/ ,3/ )-12a with (2/ )-selectivity E = 73 at —20°C) (Scheme 2). Compound ( )-ll was prepared conveniently via diastereos-elective addition of MeMgBr to t-butyl 3-phenyl-2//-azirine-2-carboxylate, which was successfully prepared by the Neber reaction of oxime tosylate of t-butyl... 

As expected, other enol ethers work well in these procedures. For example, Jones and Selenski find that implementation of method F, which occurs by addition of MeMgBr to benzaldehyde 5 in the presence of dihydropyran (DHP) at 78 °C affords a 66% yield of the corresponding tricyclic ketal 59 with better than 50 1 endo diastereoselectivity (Fig. 4.31).27 On the contrary, Lindsey reports use of method H with the benzyl alcohol 35 and diethylketene acetal. The cycloaddition reaction occurs almost instantaneously upon deprotonation of the benzyl alcohol 35 by f-butyl-magnesium bromide in the presence of the ketene acetal and yields the corresponding benzopyran ortho ester 60 in a 67% yield.29... 

In 1966, House and coworkers observed that the reaction of MeLi or MeMgBr with frawi-3-penten-2-one trans enone) in diethyl ether gave the 1,2-addition product, whereas the addition of copper salts changed the product to predominantly (MeMgBr) or exclusively (MeLi) 1,4-adduct . A copper reagent, like Li Me2Cu", was presumed, which... 

These conditions resulted also in high selectivities when Grignard reagents with different linear alkyl chains were used, whereas the substrate scope included a variety of aliphatic linear enones (Scheme 4). Particularly noteworthy is the addition of MeMgBr (e.g. to octenone), which provides the corresponding ketones with 97-98% ee, even when only 1 mol% of catalyst is employed. ... 

Cross-coupling of allylic compounds occurs by transmetallation between 7i-allyl intermediates and organometallic compounds of Mg, Zn, B, Al, Si and Sn, and subsequent reductive elimination. Reaction of the allylic dithioacetal 180 with MeMgBr in the presence of an Ni catalyst affords alkenes 184 bearing a tert-butyl group [90]. In this reaction, generation of the 7i-allylnickel 181 by oxidative addition and subsequent transmetallation with MeMgBr afford 182. Then the methylated product 183 is formed by reductive elimination, and finally the dimethylated product 184 is formed by the sequence of similar reactions. 

The CpRe-Lewis acid shown in Sch. 25 forms stable complexes with cyclohexenone and cyclopentenone. The enones coordinate to the metal forming an Re-O cr-bond. Addition of organocuprates followed by treatment with HI yield enantiomerically enriched 3-alkylated cycloalkanones and an optically active Re-I complex. MeMgBr-ether and MeLi-ether gave low yields in these reactions. The data shown in Sch. 25 reflect the problem that the yields and enantioselectivity of the organocuprate additions vary widely with the reaction conditions used and the preparation of the organocuprate [122], and must be optimized for every reaction. 

Bicyclic oxazolidinones derived from carbohydrates have been used as chiral auxiliaries in conjugate addition reactions [147]. After deprotonation with MeMgBr, the D-galacto-oxazolidin-2-one 178 and the D-g/wc6>-oxazolidin-2-one 179 (Figure 10.17) were A-acylated with... 

The first step is a simple addition we used NaCN and HOAc in Chapter 6. The second is a nitrile reaction with ethanol - an acid-catalysed addition introduced on p. 294 of the text. FtnaUy, there is a double addition of a methyl-metal compound such as MeLi or MeMgBr. The first molecule substitutes at the ester and the second adds to the resulting ketone. This reaction appears on p. 297 of the chapter. 

---