Rearrangements Grignard reagents

With a Grignard reagent, rearrangement occurs faster than addition to the epoxide, and then the Grignard reagent adds to the aldehyde. 

Of the Grignard reagent rearrangements noted thus far, some, such as those in Eqs. (9) and (12) proceed essentially to completion in the direction of cyclization. Others, for instance Eqs. (4) or (20), favor ring cleavage. The position of the equilibrium depends upon several factors. Two dominant ones are ring strain and the enthalpy change in the addition process ... 

Since Roberts observed the cyclopropylmethyl I-but-3-enyl Grignard reagent rearrangement in I960, the cyclization of unsaturated Grignard... 

Conjugate addition of vinyllithium or a vinyl Grignard reagent to enones and subsequent oxidation afford the 1.4-diketone 16[25]. 4-Oxopentanals are synthesized from allylic alcohols by [3,3]sigmatropic rearrangement of their vinyl ethers and subsequent oxidation of the terminal double bond. Dihydrojasmone (18) was synthesized from allyl 2-octenyl ether (17) based on Claisen rearrangement and oxidation[25] (page 26). 

Grignard reagent comes from the substitution products it gives with various reactive substrates. When the low-temperature adduct is heated in an autoclave at 90 to 170 C for 3 to 6 hr, it does not rearrange to 2-ethylthiazole (12) as is the case in the pyridine series (436). 

In some cases products of rearrangement are obtained either partially or exclusively on treatment of Grignard reagents with epoxides. Thus, reaction of the 2/ ,3/ -epoxide (14) with methyl Grignard reagent affords a mixture of two epimeric secondary A-nor alcohols (15) in 80% yield and the tertiary hydroxy compound, 2a-methyl-5a-cholestan-2/f-ol (16) in 15 % yield. ... 

The steroid epoxide rearrangement can occur with Grignard reagents only if both carbons of the epoxide ring are secondary. 

The formation of a library of 2-substituted quinolines employed a variation on the Boekelheide reaction. Treatment of A-oxide 41 with isobutylchloroformate did not result in the typical rearrangement. However, subsequent exposure to Grignard reagents resulted in loss of the carbonate with concomitant formation of the 2-substitute derivatives 42. 

The Grignard reagent from 2-thenyl chloride can be obtained by the use of the "cyclic reactor.However, rearrangement occurs in its reaction with carbon dioxide, ethyl chlorocarbonate, acetyl chloride, formaldehyde, and ethylene oxide to 3-substituted 2-methylthio-phenes, Only in the case of carbon dioxide has the normal product also been isolated. 

The conversion of a 4-arylazo-5-oxazolone into a 1,2,4-triazole by reaction with a Grignard reagent is mentioned in Section II, B, 3. In HiTnilar fashion, the rearrangement of compound 30 to derivatives of 3-carboxy-l,5-diphenyl-lfl -l,2,4-triazoles (40) proceeds readily in the presence of strong nucleophiles [Eq. (26)]. This transformation undoubtedly occurs by ring opening and dehydrative cychzation, and, indeed, the acyclic amide and hydrazide 41 have been isolated. ... 

Treatment of (—)-(S)-276 with allyl Grignard reagents gives optically active allylic sulphoxides 288. This reaction, however, involves an allylic rearrangement via transition state 289 as evidenced by Mislow and his collaborators362 (equation 160). 

Grignard reagents in the presence of a nickel complex to give both normal products and the products of allylic rearrangement. 

If the rearrangement of oxime sulfonates is induced by organoaluminum reagents,the intermediate (71) is captured by the nucleophile originally attached to the Al. By this means an oxime can be converted to an imine, an imino thioether (R—N—C—SR), or an imino nitrile (R—N—C—In the last case, the nucleophile comes from added trimethyl si lyl cyanide. The imine-producing reaction can also be accomplished with a Grignard reagent in benzene or toluene. ... 

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