3- butenylmagnesium chloride

In the reaction of simple 2-alkenals and a./J-unsaturated ketones with 2-butenylmagnesium chlorides essentially no diastereoselectivity is achieved it is improved by sterically highly demanding substituents adjacent to the carbonyl group43. 

Inversion of the regioselectivity in the addition of 2-butenylmagnesium chloride to aldehydes in favor of the a-adducts is caused by aluminum trichloride. A typical experiment is shown24 ... 

Butenylmagnesium chloride converts aromatic nitro compounds 383 (Ar = 2-Me(V I I4. 2- or 4-CIC6H4 or 2.6-Mei(VJ h) into the nitrones 384 aliphatic nitro compounds 385 (R = Pr or C5H11) yield allyl nitrones 386 in this reaction425. 

Butenyllithium and butenylmagnesium chloride were used as "dynamic allylic compounds. The former was selected because of the ability of lithium catalysts to provide high rates of diene polymerization and to give stereoregular polymers the latter was selected for its availability and simplicity of synthesis. 

Experimental. Butenylmagnesium chloride was prepared from crotyl chloride and magnesium chips in ether. Decomposition reactions of butenylmagnesium chloride were carried out at room temperature using H20 and D20. Butenes were condensed at — 20 °C. and analyzed on a FB-4 Shandon ionization chromatograph. 

Our NMR spectrum of butenyllithium in dimethyl ether (Figure 1) is similar to the spectrum given in Ref. 7 this spectrum and the spectrum of butenylmagnesium chloride are considered typical for such compounds. 

With butenylmagnesium chloride and butenyllithium attempts to obtain spectra of each isomer failed. Hence, an approximate method was... 

Data on the deuterolysis of butenylmagnesium chloride allow us to draw the same conclusions—i.e., the CHD/CH2D ratio, determined from the NMR spectra of deuterated butenes, supports the assumption of addition through the 7r-bond. 

For field applications, we normally use component XV as a mixture with its biologically less active stereoisomers. Our most practical route (Figure 7) to material suitable for commercial use produces a mixture which is only partially enriched in the J5 isomer at C-3 (52 see also 53). Commercially available (S)-(-)-citronellol of moderate optical purity (ca. 75% enantiomeric excess 54) is used as the starting material. The copper(I) catalyzed addition of 3-butenylmagnesium chloride to 6,7-epoxy-... 

Further interest has been taken in the chemistry of scale insects and mealybugs. All four diastereoisomers of 3-methyl-6-isopropenyl-9-decen-l-yl acetate (59), a component of the pheromone of the California red scale insect, Aonidiella aurantii, have been prepared.(S)-(-)-Citronel1ol was epoxidised followed by copper-catalysed reaction with 3-butenylmagnesium chloride to yield (58) (Scheme 10). Following dehydration and removal of the component containing the tetra-substituted double-bond by epoxidation, (3S, 6 5)-(59) was obtained. Further separation into the active enantiomer (35,6fl) followed a h.p.l.c. procedure. 

Methyl-2-butenylmagnesium chloride allowed to react 2 hrs. at 0° with 0.5 equivalent n-heptyl bromide in tetrahydrofuran in the presence of Cul 2-... 

Ketone 13 possesses the requisite structural features for an a-chelation-controlled carbonyl addition reaction.9-11 Treatment of 13 with 3-methyl-3-butenylmagnesium bromide leads, through the intermediacy of a five-membered chelate, to the formation of intermediate 12 together with a small amount of the C-12 epimer. The degree of stereoselectivity (ca. 50 1 in favor of the desired compound 12) exhibited in this substrate-stereocontrolled addition reaction is exceptional. It is instructive to note that sequential treatment of lactone 14 with 3-methyl-3-butenylmagnesium bromide and tert-butyldimethylsilyl chloride, followed by exposure of the resultant ketone to methylmagnesium bromide, produces the C-12 epimer of intermediate 12 with the same 50 1 stereoselectivity. 

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