ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Conversion of the Diastereoisomeric 12-and 6-membered 1-Acetyl-2-methyl-1-cycloalkanols to 1-Ethynyl-2-methyl-1-cycloalkenesThis paper is concerned primarily with a derivation of the E-configuration of 1-ethynyl-2-methyl-1-cyclododecene (10), which plays a role in mechanistic considerations on a method for ring expansion by 3 carbon atoms described in apreceding paper [1]. The derivation is based on an argument using the results of the dehydration of trans-1-acetyl-1-2-methyl-1-cyclododecanol (4) to 10 with phosphorus oxychloride and pyridine. That this dehydration is stereospecific can be concluded from its regiospecificity since the cis-hydroxyketone 3 dehydrates mainly to 1-ethynyl-12-methyl-1-cyclododecene (mixture of stereoisomers 11 and 12). An x-ray analysis shows the indicated configurations of the two hydroxyketones 3 and 4.The direction (anti) of the stereospecificity of the double bond introduction during the 4→10 conversion is deduced from the similarity of the behaviour of the two stereoisomeric 1-acetyl-2-methyl-1-cyclohexanols 8 and 9 under the same conditions and from mechanistic considerations, which make it likeley that the anti-elimination behaviour observed in the 6-membered system has not changed over to a syn-elimination behaviour in the 12-membered system. The configurations of the two 6-membered hydroxyketones 8 and 9 correspond to those of the precursor1-ethynyl-2-methyl-1-cyclohexanols 6 and 7, which were clarified with the help of 13C-NMR.-spectral coupling observations.It is of interest that the hydroxyketones 3, 4, 8 and 9 react with phosphorus oxychloride and pyridine so as to introduce both a double and a triple bond. It is probable that the double bond is introduced first, inasmuch as the triple bond is not introduced in the absence of activation of the hydroxyl group, as for instance in acetylcyclohexane. This can be used as an argument that the conversion of the acetyl to an ethynyl group in 3, 4, 8 and 9 does not affect the stereospecificity of the dehydration which introduces the ring double bond.1-Acetyl-2-methyl-1-cyclododecene (24), a previously isolated compound with pleasant odor, was synthesized by hydration of 10. This furnishes an argument for the E-configuration of 24.
Additional Material:
3 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19780610145
