Solved: Propose a plausible mechanism for the following

Provide a systematic name for each of the following compounds: (a) (b) Cl Cl (c) Br (d)

Draw a bond-line structure for each of the following compounds: (a) 2-Heptyne (b) 2,2-Dimethyl-4- octyne (c) 3,3-Diethylcyclodecyne

Predict the product for each of the following reactions: H2 Lindlars catalyst Na NH3 (l) ? H2 Pt ? ?

Predict the product for each of the following reactions: H2 Lindlars catalyst H2 Pt ? ?

Draw the products of each of the following acid-base reactions and then predict the position of equilibrium in each case: H H + (a) Li @ ! H + NaH (b)

Predict the products obtained when 1-pentyne reacts with each of the following reagents: (a) H2SO4, H2O, HgSO4 (b) 9-BBN followed by H2O2, NaOH (c) Two equivalents of HBr (d) One equivalent of HCl (e) Two equivalents of Br2 in CCl4 (f) NaNH2 in NH3 followed by MeI (g) H2, Pt

Identify the reagents you would use to achieve each of the following transformations: CH3 O O H Br Br OH O Cl

2 Identify which of the following bases can be used to deprotonate a terminal alkyne: (a) NaOCH3 (b) NaH (c) BuLi (d) NaOH (e) NaNH2

Identify which of the following compounds represent a pair of keto-enol tautomers: OH O (a) OH O (b) OH O (c) HO OH O OH (d)

Draw the enol tautomer of each of the following ketones: O (a) O (b) O (c)

Oleic acid and elaidic acid are isomeric alkenes: OH O Oleic acid OH O Elaidic acid Oleic acid, a major component of butter fat, is a colorless liquid at room temperature. Elaidic acid, a major component of partially hydrogenated vegetable oils, is a white solid at room temperature. Oleic acid and elaidic acid can both be prepared in the laboratory by reduction of an alkyne called stearolic acid. Draw the structure of stearolic acid and identify the reagents you would use to convert stearolic acid into oleic acid or elaidic acid.

Predict the final product(s) for each sequence of reactions: Br Br 1) Excess NaNH2 2) EtCl 3) H2 (a) , Lindlars catalyst ? H C C H 1) NaNH2 2) MeI 3) 9-BBN 4) H2O2 (b) , NaOH ? H C C H 1) NaNH2 2) EtI 3) HgSO4, H2SO4 (c) , H2O ? H C C H 1) NaNH2 2) MeI 3) NaNH2 4) EtI 5) Na, NH3 (l) ? (d)

When (R)-4-bromohept-2-yne is treated with H2 in the presence of Pt, the product is optically inactive. Yet, when (R)-4-bromohex- 2-yne is treated with the same conditions, the product is optically active. Explain.

Draw the structure of an alkyne that can be converted into 3-ethylpentane upon hydrogenation. Provide a systematic name for the alkyne.

Propose a mechanism for each of the following transformations: (a) NH3 (l) Na HO OH O O H3O+ (b)

Draw the expected product of each of the following reactions, showing stereochemistry where appropriate: Cl H D NaNH2 NH3 ?

Compound A is an alkyne that reacts with two equivalents of H2 in the presence of Pd to give 2,4,6- trimethyloctane. (a) Draw the structure of compound A. (b) How many chirality centers are present in compound A? (c) Identify the locants for the methyl groups in compound A. Explain why the locants are not 2, 4, and 6 as seen in the product of hydrogenation.

Compound A has molecular formula C7H12. Hydrogenation of compound A produces 2- methylhexane. Hydroboration-oxidation of compound A produces an aldehyde. Draw the structure of compound A and draw the structure of the aldehyde produced upon hydroborationoxidation of compound A.

Propose a plausible synthesis for each of the following transformations: O (a) (b) Br Br (c) Br Br (d) Cl Cl O Br Br Br Br (e) (f) Cl Cl OH

4 1,2-Dichloropentane reacts with excess sodium amide in liquid ammonia (followed by water workup) to produce compound X. Compound X undergoes acid-catalyzed hydration to produce a ketone. Draw the structure of the ketone produced upon hydration of compound X.

An unknown alkyne is treated with ozone (followed by hydrolysis) to yield acetic acid and carbon dioxide. What is the structure of the alkyne?

Compound A is an alkyne with molecular formula C5H8. When treated with aqueous sulfuric acid and mercuric sulfate, two different products with molecular formula C5H10O are obtained in equal amounts. Draw the structure of compound A, and draw the two products obtained.

7 Propose an efficient synthesis for each of the following transformations: (a) (b) O (c) (d)

Draw the structure of each possible dichloride that can be used to prepare the following alkyne via elimination:

Draw the structures of compounds A to D: A (C6H12) B C 1) Excess NaNH2 2) H2O Br2 NaNH2 D I

Identify the reagents necessary to achieve each transformation below. In each case, you will need to use at least one reaction from this chapter and at least one reaction from the previous chapter. The essence of each problem is to choose reagents that will achieve the desired stereochemical outcome: Br (a) Br Br Br + En (b) OH OH + En (c) OH (d) OH OH OH + En (e) OH (f) OH

Identify the reagents necessary to achieve each transformation below: D D (a) D D (b) D (c)

The following reaction does not produce the desired product but does produce a product that is a constitutional isomer of the desired product. Draw the product that is obtained and propose a mechanism for its formation: OH OH 1) NaNH2 2) MeI

Propose a plausible mechanism for the following transformation: O OH O OH H3O+

Propose a plausible mechanism for the following tautomerization process: N H CH3 N CH3 H3O+

sing acetylene and methyl bromide as your only sources of carbon atoms, propose a synthesis for each of the following compounds: O Et Me + En (a) O Et Me + En (b

Propose a plausible mechanism for the following transformation: R R O Br H3O+ Br2

Propose a plausible mechanism for the following transformation: D O O H D3O+

Roquefortine C belongs to a class of natural products, called roquefortines, first isolated from cultures of the fungus Penicillium roqueforti. Roquefortine C, which is also present in blue cheese, exhibits bacteriostatic activity (it prevents bacteria from reproducing), and it is known to exist as a mixture of two tautomers, as shown below (J. Am. Chem. Soc. 2008, 130, 62816287): N N N H O O H H Roquefortine C HN N N N N H O O H H N NH taut. (a) Draw a base-catalyzed mechanism for the tautomerization of roquefortine C. (b) Draw an acid-catalyzed mechanism for the tautomerization of roquefortine C. (c) Predict which tautomer is more stable and explain your rationale.

A small class of natural products, called a,a-disubstituted a-amino acids (Chapter 25), have been the targets of several synthetic techniques, because these compounds are structurally complex (representing a challenge for synthetic organic chemists), and they exhibit notable effects on biological activity. The following transformation was part of one such synthetic technique (Org. Lett. 2003, 5, 40174020): (a) Identify reagents that can be used to achieve the following transformation and (b) assign the configuration of the chirality center in the starting material and in the final product. (BOC)2N (BOC)2N O O CH3O CH3O CH3O CH3O Si BOC = t-BuO O O O OSiMe2t-Bu OCH3 3 2

Natural products that contain the N-1,1-dimethyl-2-propenyl group (called an N-reverse prenyl group) often exhibit antitumor or antifungal activity. The synthesis of a particular N-reverse prenylated indole antifungal compound begins with the two steps shown below (Tetrahedron Lett. 2001, 42, 72777280): N H OAc OAc = N O O 1 2 3 C13H15N CuCl, i-Pr2NEt (a) Draw the structure of compound 2 and show a reasonable mechanism for its formation. Note that i-Pr2NEt is a base, and CuCl is used as a catalyst. The latter can be ignored for our purposes. (b) Identify the reagents necessary for the conversion of 2 to 3.

Treatment of one mole of dimethyl sulfate (CH3OSO3CH3) with two moles of sodium acetylide results in the formation of two moles of propyne as the major product (J. Org. Chem. 1959, 24, 840842): (a) Draw the inorganic, ionic species that is generated as a byproduct of this reaction and show a mechanism for its formation. (b) 2-Butyne is observed as a minor product of this reaction. Draw a mechanism accounting for the formation of this minor product and explain how your proposed mechanism is consistent with the observation that acetylene is present among the reaction products. (c) Predict the major and minor products that are expected if diethyl sulfate is used in place of dimethyl sulfate.

Salvinorin A, isolated from the Mexican plant Salvia divinorum, is known to bind with opioid receptors, thereby generating a powerful hallucinogenic effect. It has been suggested that salvinorin A may be useful in the treatment of drug addiction. Terminal alkyne 2, shown below, was used in a total synthesis of salvinorin A (J. Am. Chem. Soc. 2007, 129, 89688969). Propose a plausible mechanism for the formation of 2 from alkyne 1. (Hint: refer to Problem 10.8). OH O OH O 1 2 1) NaNH2 2) H2O

Halogenation of alkynes with Cl2 or Br2 can generally be achieved with high yields, while halogenation of alkynes with I2 typically gives low yields. However, the following reaction is successfully completed with I2 in high yields (94%) to afford a potentially useful functionalized and conformationally constrained diiododiene synthetic intermediate (Tetrahedron Lett. 1996, 37, 15711574). Propose a plausible mechanism for this transformation. I2 I I

The following compounds exhibit tautomerism, with a particularly high enol concentration. Compound 1 exhibits an enol concentration of 9.1%, as compared with the enol concentration of 0.014% for (CH3)2CHCHO. Compound 2 exhibits an enol concentration of 95% (Acc. Chem. Res. 1988, 21, 442449): 1 2 O H O H (a) Draw the enol of compound 1 and offer an explanation for the high enol concentration, relative to (CH3)2CHCHO. (b) Draw the enol of compound 2, and explain why the enol is favored over the aldehyde in this case.

The two lowest energy conformations of pentane are the anti-anti and the anti-gauche forms, in terms of arrangements around the two central C!C bonds. A recent study analyzed the conformations of 3- heptyne as an elongated analogue of pentane, where a carbon-carbon triple bond is inserted between C2 and C3 of pentane (J. Phys. Chem. A. 2007, 111, 35133518). Interestingly, the researchers found that in each of the two most stable conformations of 3-heptyne, C1 and C6 are nearly eclipsed (looking down the alkyne group). In one of these conformations, C4 and C7 are anti to each other (looking down the C5C6 bond); and in the other conformation, C4 and C7 experience a gauche interaction. Draw the following: (a) A wedge-and-dash structure for each of the two lowest energy conformations of pentane (b) A wedge-and-dash structure of the conformer of 3-heptyne that is analogous to anti-anti pentane (c) A Newman projection that illustrates the eclipsed nature of the low-energy conformations of 3-heptyne (d) Newman projections that illustrate the difference between the two lowest energy conformations of 3-heptyne

A variety of phenyl-substituted acetylenes (1ad) were treated with HCl to give a mixture of E and Z isomers, as shown below (J. Am. Chem. Soc. 1976, 98, 32953300): C C R HCl C C H R Cl + C C R H Cl E:Z Ratio 1a (R = Me) 70:30 1b (R = Et) 80:20 1c (R = i-Pr) 95:5 1d (R = t-Bu) 100:0 1 (a) Draw the two possible vinyl carbocations that can form when phenyl-substituted acetylenes are protonated by HCl and explain the regioselectivity observed in these reactions. (b) By comparing transition state stabilities for the step in which the most stable vinyl carbocation is captured by a chloride ion, provide an explanation for the stereoselectivity (the E:Z ratio) observed in the reactions of 1ad.

The compound 1,2-bis-(phenylethynyl)benzene (1) undergoes reactions with aqueous acid or bromine, as shown below (J. Am. Chem. Soc. 1966, 88, 45254526). Propose a reasonable arrow- pushing mechanism for both of these reactions. Also provide an explanation for the configuration of the exocyclic alkene (the one that is external to the ring) in the product of the bromination reaction. Br Br 1 H2SO4 H2O Br2 O