L-Hepten-6-ynes

The nature of the transition state in the 3,3-shift was examined by Berson who found that (5 )-4-methyl-2-hepten-6-yne gave recovered starting material and both RZ)- and (5 )-4-methyl-l,2,5-heptatriene and the latter two gave (/ Z)-4-methyl-2-hepten-6-yne all reversibly with high stereospecificity prior to formation of cyclized and dimeric products (Scheme 7.51). These results are consistent with an allowed stereopathway via a chair-like transition state as opposed to a forbidden one or the one in which an effectively planar cyclohexene-1,4-diyl is involved. 

The method for naming alkynes, with a general formula of C H2 2> is essentially the same as that for alkenes. Figure 3.29 shows the lower members of the family. Notice that the triple bond is always drawn as linear. Find the longest chain that contains the triple bond, and number the chain so that the triple bond has the lowest number. Then add substituents as before. So 3.40 is 6-methyl-3-octyne. When there is both an alkene double bond and an alkyne triple bond in the molecule, as in 3.41, the alkene takes precedence in nomenclature. So 3.41 is l-heptene-3-yne. 

Racemic isohumulone is prepared from the key product 2-methyl-2-penten-4-yne, which is obtained by a 1,4-elimination reaction from 1-bromo-4-methylpenta-1,2-diene, in the presence of copper(l) cyanide (85). Addition of the hydrocarbon to ethyl pyruvate, followed by hydrolysis, leads to 2,6-dimethyl-2-hydroxy-5-hepten-3-yne acid. The corresponding acid chloride is added to ethyl 3-oxo-5-methylhexanoate in the presence of magnesium methylate. The reaction product cyclizes in basic medium to... 

Bromo-4-chloro-6-fluorophenol 4-Methyl-tra 5-2-heptene 1,4-Cyclohexadiene 2-Methyl-l-hexene-4-yne 1,3,5-Tribromobenzene... 

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