Grignard reagent to olefins

Grignard reagent in the preparation of a hydrocarbon, 4, jg Grignard reagent to olefins, 6, 32 Guaiacol, 3, 28 Guanidine, 7, 69... 

This Table was published in Tetrahedron Letters, H. Schafer and H. Kiintzel, Anodic addition of Grignard-reagents to olefins , 3333-3336, Copyright Elsevier, 1970. 

Ethers, such as tetrahydrofuran and 1,2-dimethoxyethane, have low dielectric constants (7.4 and 7.2, respectively), and the choice of supporting electrolyte is very limited. The ethers are difficult to reduce and are inert toward many metalorganic reagents [243] that are soluble in the ethers. Ethers are thus suitable as medium for the anodic addition of Grignard reagents to olefins [420]. Dimethoxyethane and polyethylene glycol dimethyl ethers have the ability to solvate electrons [421]. Dissociation constants for some acids and the relative strength of some bases in THE has been determined [422]. 

This reaction is extended to the intramolecular ring closure of the intermediate radical 224 with olefinic or trimethylsilylacetylenic side chains [121]. Cu(BF4)2 is also effective as an oxidant (Scheme 89) [122]. Conjugate addition of Grignard reagents to 2-eyclopenten-l-one followed by cyclopropanation of the resulting silyl enol ethers gives the substituted cyclopropyl silyl ethers, which are oxidized to 4-substituted-2-cyclohexen-l-ones according to the above-mentioned method [123]. (Scheme 88 and 89)... 

Fig. 8.28. Preparation of an olefin by adding a Grignard reagent to a ketone and subsequent workup with a strong acid.

Trichlorotrifluoroethane and zinc in diethyl ether or dimethylfor-mamide (DMF) form an organometallic complex with diethyl ether [773] or dimethylformamide [114. This complex reacts with aldehydes similarly as the Grignard reagents to form primarily the expected alcohols. In the presence of acetic anhydride, the alcohol is converted to the corresponding olefin, predominantly with Z configuration. In the case of benzaldehyde, Z- and E- 2-chloro-l-phenyl-3,3,3-trifluoropropene are the products H and I [114]. 

This reaction is superficially understood as a formal delivery of H-MgX element from a Grignard reagent to an olefin under catalysis of such a transition metal complex (Scheme 3). 

Rearrangements are common in transition metal chemistry, and it is not within the scope of this discussion to cover this topic. However, many of these rearrangements occur to increase the electron density on the metal center. An example of this concept is addition of allylic Grignard reagents to a metal-centered electrophile. Typically an // -complex is formed from the expected a-bond that is formed, followed by coordination of the olefin as a 7c-bond, which is better represented as an // -complex [Eqs. (57-59) 160-162]. 

There are numerous accounts of intramolecular addition of Grignard reagents to unconjugated olefins, and several reviews have appeared [2,5,16,17], Examples of these include both terminal olefins [Eq. (3) 18] and internal olefins [Eq. (4) 19] ... 

The addition of Grignard reagents to enones has been extensively studied and reviewed [6-12] (see also Chapter 16). Enones can react either as carbonyls or olefins, leading to 1,2-addition (to the carbonyl) or 1,4-addition (to the olefin Scheme 2). 

A carbonyl transposition can be effected via the addition of a vinyl or an alkyl Grignard reagent to an a, 3-unsaturated ketone. Acid-catalyzed rearrangement of the resultant allylic alcohol during oxidation with PCC affords the transposed a,(3-unsaturated carbonyl substrate. This reaction represents a useful alternative when Wittig olefination of the ketone is problematic. 

In many cases of addition to an a,/3-unsaturated compound we cannot be sure whether addition takes place at the olefin double bond (i.e., 3,4-addition) or whether the preliminary step involves 1,4-addition followed by ketonization. Thus for the addition of a Grignard reagent to the... 

Miscellaneous. The addition of Grignard reagents to the functionalized phosphines (93) leads to the magnesium alkoxides (94), which react with methyl iodide selectively at phosphorus. The magnesium salts (95) of the resulting betaines undergo elimination, on heating with potassium t-butoxide, to form the olefins (96) and methyldi-phenylphosphine oxide.i ... 

---