L- pentyne

The alkane formed by hydrogenation of (S)-4-methyl-l-hexyne is optically active, but the one formed by hydrogenation of (S)-3-methyl-l-pentyne is not. Explain. Would you expect the products of hydrogenation of these two compounds in the presence of Lindlar palladium to be optically active ... 

Ketones react with acetylide ion (Section 8.7) to give alcohols. For example, the reaction of sodium acetylide with 2-butauone yields 3-methy -l-pentyn-3-ol ... 

The well documented synthetic method for 37 is chlorination of cyclopropyl-methylketone followed by base treatment [29]. However, this method did not provide a suitable impurity profile. The most convenient and suitable method we found was the one-step synthesis from 5-chloro-l-pentyne (49) by addition of 2equiv of base, as shown in Scheme 1.18 [21, 30]. Two major impurities, starting material 49 and reduced pentyne, had to be controlled below 0.2% each in the final bulk of 37, to ensure the final purity of Efavirenz . Acetylene 37 was isolated by distillation after standard work-up procedure. 

Fig. 13. Tilted 2D spectrum of natural abundance 2H Q-COSY experiment of ( )-l-pentyn-ol dissolved in PBLG/chloroform chiral nematic liquid crystal. The spectrum was symmetrized prior to the tilting procedure. Note that all isotopomers of the mixture are clearly visualized. (Reproduced by permission of American Chemical Society.)...

Presence of a certain type of functional groups in alkynes does not interfere with silylformylation. For example, the chlorine atom in 5-chloro-l-pentyne 44 and the cyano group in 5-cyano-l-pentyne 46 do not affect the silylformylation to give 45 and 47 respectively (Equations (10) and (11)). 4-Bromo-l-butyne and 6-bromo-l-hexyne also give the corresponding silylformylation products." ... 

Similarly, if 5-iodo-l-pentyne (66) was converted to the alkynylethylzinc reagent 67, the subsequent Zr-promoted ethylzincation afforded the gem-diorganozinc 68 which was stable in dichloromethane. Replacement of the latter by a more basic solvent such as THF triggered a a-type cyclization process leading to the cyclopentenylzinc 69, as demonstrated by the formation of 70 after iodinolysis (equation 27)45. 

It is also possible to achieve the formation of five-membered rings by coupling the allylzincation of a metallated alkyne with an intramolecular nucleophilic substitution. Thus, allylzincation of the ethylzinc alkynylide generated from 5-iodo-l-pentyne (66)45, or direct treatment of the latter with excess crotylzinc chloride177, led to the alkenyl... 

N-Methyldipicrylamine. See 2,4,6,2, 4, 6 -Hexanitro-N-methyl-diphenylamine A440-R 3-Methyl-3-hydroperoxy-I-butyne. See under Acetylene Hydroperoxides A66-L 3-Methyl-3-hydroperoxy-l-pentyne. See under Acetylene Hydroperoxide A66-L o-Methylisoxazolecarboxylic Acid. See under Acetylene-Nitric Acid Reaction Studies... 

The first "tandem reactions forming geminal carbon-carbon bonds" were reported in 1991, and the following example is representative. A mixture of 5-iodo-l-pentyne (1 eq.) and p-fluorophenyl isocyanide (5 eq.) in t-butylbenzene containing hexamethylditin (1.5 eq.) was irradiated under nitrogen in a pyrex flask at 150°C for several hours until all of the alkyne had been consumed (followed by H nmr). Standard work up gave a mixture of the cyclopentaquinolines 1 and 2 in 56% yield and 85/15 ratio. 

The alkane formed by hydrogenation of (5 )-3-methyl-l-pentyne is achiral it cannot be optically active. 

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