Vinylmagnesium

Finally (d + aV dditions of 1-alkenyl and 1-alkynyl anions to carbonyl groups should be mentioned. Examples are the addition of vinylmagnesium bromide to ketones e.g. in the first step of Torgov s steroid synthesis (I.N. Nazarov, 1957), and the famous alkynylation of... 

Vibrational relaxation, 293, 295 17 a-Vinyl-5a-androstane-3 /3,17 /3-diol, 164 Vinyllithium, 64, 163 Vinylmagnesium chloride, 58 4-Vinyltestosterone, 89... 

In 1989, Bartoli reported that vinylmagnesium bromide reacted with 2-nitrotoluene (4) at -40 C in THF to furnish 7-methylindole (5) in 67% yield. The reaction process also proceeded well with other 2-substituted nitrobenzenes. However, the 3- or 4-substituted nitrobenzenes provided either no indole products or indoles in poor yield. ... 

Vinylmagnesium bromide (15 mmol) was quickly added to a stirred solution (10 mL/mmol) of 2-nitrotoluene (4) (5 mmol) in THF cooled at -40 C under nitrogen. The reaction mixture was stirred for 20 minutes and then poured into a saturated aqueous... 

In the first of these sequences, often called the Torgov-Smith synthesis, the initial step consists in condensation of a 2-alkyl-cyclopentane-l,3-dione with the allyl alcohol obtained from 6-methoxy-l-tetralone and vinylmagnesium chloride. Although this reaction at first sight resembles a classic SN displacement, the reaction is actually carried out with only a trace of base. 

Scheme 2.23 Aziridination of aji-unsaturated hydrazones with vinylmagnesium bromide.

The addition of vinylmagnesium bromide to methyl (S)-3-benzyloxy-4-oxobutanoate (5) in tetrahydrofuran proceeded with a slight preference for the nonchelation-controlled reaction product (40 60)5°. A reversal of the diastereoselectivity (80 20) could be observed when the Grignard reagent, as a solution in tetrahydrofuran, was added to a dichloromethane solution of the aldehyde which had been precomplexed with one equivalent of magnesium bromide. The almost exclusive formation of the chelation-controlled reaction product 6 was achieved when tetrahydrofuran was completely substituted by dichloromethane the presence of tetrahydrofuran interferes with the formation of the chelate complex, which is a prerequisite for high chelation-controlled diastereoselection. 

Whereas the nucleophilic addition of vinylmagnesium bromide to a-alkoxy aldehydes (12, 16) proceeds with a low to moderate chelation-controlled diastereoselectivity, a remarkably high preference for the opposite stereochemical behavior is found with the jS-silyl phosphorus ylide 1477. Due to the electron-donating 4-methoxyphenyl substituents at the phosphorus atom, as well as the /i-methyldiphenylsilyl group, 14 is an excellent vinylation reagent which does not lead to any Wittig olefination products. 

As with oxathianes 3 (R1 = CH, R2 = H), which bear a close structural resemblance to 17, the addition of organometallic reagents is highly diastereoselective with a predominant chelation-controlled attack of the nucleophile from the Rc-sidc35 -40. In the case of vinylmagnesium bromide a considerable enhancement of the diastereo selectivity could be attained by adding... 

Tributyl(l-ethoxy-2-propenyl)stannane (2) was first prepared from tributyl[chloro(ethoxy)-methyl]stannane and vinylmagnesium bromide, and found to be unstable with respect to 1,3-migration of the tributyltin substituent101. Tributyl(l-ethoxy-3-methyl-2-butenyl)stannane (1) was found to be more stable, and has since been prepared directly from (tributyl)(diethoxy-methyl)stannane and 2-methylpropenylaluminum dichloride generated in situ102. 

C15H24O 520S-9J-5) see Isotretinoin Retinol Tretinoin vinylmagnesium bromide... 

Vinyl acetate, 57,117 Vinylacetic acid, 56,49 ct-Vinylbenzyl alcohol, 56, 106 Vinyl bromide, 58,152, 155, 157 Vinyl chloride, 58,133 Vinylene carbonate, 57, 117 Vinylmagnesium halides, 59,92 2-Vinylpytidine, 58, 73 Vinyl sulfides, 59, 202... 

In the preparation from lead(II) chloride and vinylmagnesium bromide in THF-hexane, violent explosions occurred during isolation of the product by distillation of solvent. This could be avoided by a procedure involving steam distillation of the tetravinyllead, no significant loss of yield by hydrolysis being noted. It is likely to be considerably more endothermic than tetraethyllead. 

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