4-Pentyne

To a mixture of 50 ml of dry THF and 0.050 mol of l-tert.-butoxy-2-pentyne (prepared by ethylation of HC-CCH O-tert.-Ci,H9 in liquid ammonia was added 0.055 mol of butyilithium in about 35 ml of hexane in 10 min at -30°C. After stirring for 20 min at -25°C the solution was cooled to -50°C and 0.06 mol of methyl iodide was added in one portion, followed 10 min later by 50 ml of water. The aqueous layer was separated and extracted twice with diethyl ether. The solutions were dried over magnesium sulfate and concentrated in a water-pump vacuum. 

Assume that you need to prepare 4 methyl 2 pentyne and discover that the only alkynes on hand are acetylene and propyne You also have available methyl iodide isopropyl bromide and 1 1 dichloro 3 methylbutane Which of these compounds would you choose in order to perform your synthesis and how would you carry it out" ... 

CHsCHjCHzC CH (1 pentyne) CHsCHjC CCHs (2 pentyne) (CH3)2CHC=CH (3 methyl 1 butyne)... 

C5H8 2-PENTYNE 127.758 2.1215E-01 3.2628E-Q5 194.18 247 C6H10 CYCLOHEXENE -8.701 3.7574E-01 3.5208E-05 106.86... 

Dimethylfuran, in a sensitized reaction, gave 1,3-dimethylcyclopropene (the main product), isoprene, cis- and rran.s-l,3-pentadiene, 2-pentyne, and 1-methylcyclopropenyl methyl ketone (Scheme 7) (70JPC574) the ring contraction showed a high selectivity. 

The irradiation of 2,5-dimethylfuran in the presence of mercury vapor gave a complex mixture of products. Carbon monoxide and propene were removed as gaseous products. Then, cis- and rran.s-l,3-pentadiene, isoprene, 1,3-dimethylcyclopropene, 2-pentyne, 2-ethyl-5-methylfuran, hexa-3,4-dien-2-one, 1-methyl-3-acetylcyclopropene, and 4-methylcyclopent-2-enone were obtained (Scheme 8) (68JA2720 70JA1824). The most abundantproduct was the cyclopentenone 19, the second was the 1,3-pentadiene 12, while the third product was the cyclopropenyl derivative 18. 

Hexyne, 2-hexyne, 3-hexyne, 3-methyl-Hpentyne, 4-methyl-l-pentynep 4-methyl-2-pentyne, 3.3-dimethyl-l-butyne... 

The metathesis of linear alkynes has also been reported, e.g. the metathesis of propyne, 1-pentyne, 2-pentyne, and 2-hexyne (31-33). This reaction can be visualized as the cleavage and formation of carbon-carbon triple bonds ... 

The present route to (terminal alkynes reported by a group from the Chemical Process Department at the DuPont Pharmaceutical Company.2 This alcohol serves as a convenient starting material for the preparation of 1-acyloxy 4-mesylates 10 (eq 1). 

Identify the type and number of bonds on carbon atom 2 in (a) pentane (b) 2-pentene (c) 2-pentyne. 

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