Methylmagnesium iodide, 1,4-addition

Cyanopyridazines add ammonia, primary and secondary amines and hydroxylamine to give amidines or amidoximes. Substituted amides, thioamides and carboximidates can be also prepared. With hydrazine, 3-pyridazinylcarbohydrazide imide is formed and addition of methylmagnesium iodide with subsequent hydrolysis of the imine affords the corresponding pyridazinyl methyl ketone. 

The addition of methylmagnesium iodide to 2-phenylpropanal is stereoselective in producing twice as much syn-3-phenyl-2-butanol as the anti isomer (entry 5). The stereoselective formation of a particular configuration at a new stereogenic center in a reaction of a chiral reactant is called asymmetric induction. This particular case is one in which the stereochemistry can be predicted on the basis of an empirical correlation called Cram s rule. The structural and mechanistic basis of Cramls rule will be discussed in Chapter 3. 

The stereochemistry of the 1,4-addition to A -octal-l-one and 1,1-di-methyl-A -octal-2-one has been investigated by House and Marshall, respectively. In summary, steric and stereoelectronic factors play a part in the mechanism of conjugate addition of Grignard compounds. With methylmagnesium iodide, the introduction of an axial methyl group into steroidal 5a-A -3-ketones (3) and 5 -A -3-ketones (6) is favored by stereo-electronic factors in the transition state. 

Schaub ° introduced methyl groups at both the 16a- and 17a-positions by 1,4-addition of methylmagnesium iodide to the A -20-ketone (8) followed by methylation of the intermediate 16a-methyl-17-enolate anion (9) with methyl iodide. After hydrolysis of the tetrahydropyranyl ether group a 40% yield of the 16,17-dimethyl derivative (10) was obtained. With the corresponding 3j -acetoxy derivative, the yield of (10) is only 20%. 

To a solution of 2 mols of methylmagnesium iodide in 1.5 liters of ether are added with vigorous stirring 107 g (0.5 mol) of ethyl p-chloroatrolactate. The reaction mixture is stirred for about sixteen hours, and is then decomposed by the addition of about 320 ml of saturated aqueous ammonium chloride solution. After standing, the ether layer is decanted from the mixture and the aqueous phase and the precipitated salts are washed with several 500 ml portions of ether. The combined ether solution and washings are washed with successive 500 ml portions of 5% ammonium chloride solution and water, are dried over anhydrous magnesium sulfate, and are evaporated to dryness in vacuo. The crystalline residue consisting of 2-p-chlorophenyl-3-methyl-2,3-butanediol, is recrystallized from a mixture of benzene and petroleum ether. 

Exclusive exo (equatorial) attack is also observed with bicyclo[3.2.1]octan-3-one (5), whereas addition of methylmagnesium iodide to bicyclo[3.2.1]octan-2-one (7) affords the diastereomeric products in almost equal amounts5i. The cyclohexanone moiety of both bicyclic ketones 5 and 7 adopts a chair conformation and therefore the 3,5-diaxialethano bridge in... 

Using oxathiane 11, ( + )-(i )-2-methoxy-2-phenylpropanoic acid was obtained in 97% ee, however, the synthesis contains some inconvenient reaction steps. Thus, reduction of ( + )-10-camphorsulfonic acid (8) leads in low yield to a mixture of 10-mercaptoisoborneol (9 A) and 10-mercaptoborneol (9B) which must be separated by chromatography. The oxathiane 10 resists deprotonation with butyllithium and, therefore,, y -butyllithium had to be employed. Furthermore, after addition of methylmagnesium iodide, cleavage of the oxathiane moiety 12, with iodomethane did not proceed as well as with the simpler oxathianes 3. 

Besides 1,3-oxathianes, the 1,3-dithiane 1-oxide moiety can be used for directing the nucleophilic addition of an organometallic reagent to a carbonyl group in a diastereoselective manner. The addition of methylmagnesium iodide to the 2-acyl-l,3-dithiane 1-oxide 23A leads exclusively to the diastereomer which is formed by Re-side attack. On the other hand, addition... 

The phosphonyl adduct 300 reacted with a dilute solution of anhydrous hydrogen chloride in ethanol or with sodium ethoxide to afford an essentially quantitative yield of the P-N cleaved product 304 with inversion of configuration. Addition of sodium ethoxide to a solution of 304 in methanol resulted in the formation of enantiomerically pure (+)-(.V)-ethyl methyl phenylphosphonate (305). It also reacted quantitatively with methylmagnesium iodide at room temperature to give the product of P-S bond cleavage 306, which upon acid catalyzed methanolysis afforded enantiomerically pure (+)-(R)- methyl methylphenylphosphinate (307) (Scheme 72) [108],... 

Methylmagnesium iodide reacts with the 3-carbonyl group of 243 and gives rearranged product 81. When phenylmagnesium bromide is used instead, conjugate addition occurs (Scheme 31) <1994T5037>. 

One of the important mechanisms by which orally administered steroids are inactivated involves the formation of water-soluble derivatives at the 17 position, a process that is greatly reduced in 17a-alkyl-17(3-hydroxy derivatives. Extensive use of the resulting orally active compounds has since revealed that 17 alkylation also leads to increased liver toxicity. Preparation of the first of these compounds, nor-methandrolone (32-3), starts by addition of methylmagnesium iodide to estrone methyl ether (9-1) to give the 17a methyl derivative. Birch reduction followed by acid hydrolysis leads to normethandrolone (32-3) [16]. 

Cul, methyllithium, and a camphor-derived /3-amino alcohol (239). Reaction of methylmagnesium iodide and benzylideneacetone in the presence of a small amount of a chiral Cu(I) thiolate complex gives the conjugate addition product in 57% ee (240). 

---