2.3- Dimethyl-2-butene preparation

The dimerization of propene has been extensively studied because the propene dimers are of considerable interest as fuel additives and as starting materials for the preparation of monomers (4, 48, 49, 101). The reaction course can be controlled to give methylpentenes, 2,3-dimethyl-butenes (2, 4, 7, 47, 51), or hexenes (44-46) as the main products. 

Preparation of 3,5-dimethyl-4-(trifluoromethyl)-2,5-heptadien-4-ol. A 1-L, three-necked, round-bottomed flask, equipped with a reflux condenser, a magnetic stir bar and an addition funnel is flame dried under an atmosphere of argon. After the apparatus has cooled, 350 mL of anhydrous diethyl ether (freshly distilled from sodium benzophenone10 under argon) is added. Lithium wire (6.9 g, 1.0 mol, 3.2-mm diameter, 0.01% Na content, Aldrich Chem. Co., Milwaukee, WI), which is cut into 5- to 10-mm pieces and washed with hexanes, is added to the flask under a counterstream of argon gas. The reaction flask is cooled to 0°C in an ice bath and 68.9 g (0.51 mol) of 2-bromo-cis-2-butene (prepared in the previous step9) in 50 mL of anhydrous diethyl ether is added dropwise over a 45-min period while the reaction mixture is stirred. The reaction solution becomes cloudy due to the formation of lithium bromide. Stirring is continued for an additional 1.5-2 h at 0°C. 

Monosubstituted Boranes. Only a few monoaLkylboranes are directiy available by hydroboration. Tertiary hexylborane, 2,3-dimethyl-2-butylborane [3688-24-2] (thexylborane, Thx) BH2 (5), easily prepared from 2,3-dimethyl-2-butene, is the best studied (3,60—62). It should be... 

The photolysis of a-diazosulfones dissolved in alkenes provides sulfonyl-substituted cyclopropanes in high yields. This is exemplified by the preparation of l-(p-methoxyphenylsulfonyl)-2,2,3,3-tetra-methylcyclopropane in 75% yield from -methoxybenzenesulfonyl-diazomethane and 2,3-dimethyl-2-butene. A similar addition to [Pg.101]

Due to the abundance of epoxides, they are ideal precursors for the preparation of P-amino alcohols. In one case, ring-opening of 2-methyl-oxirane (18) with methylamine resulted in l-methylamino-propan-2-ol (19), which was transformed to 1,2-dimethyl-aziridine (20) in 30-35% yield using the Wenker protocol. Interestingly, l-amino-3-buten-2-ol sulfate ester (23) was prepared from l-amino-3-buten-2-ol (22, a product of ammonia ring-opening of vinyl epoxide 21) and chlorosulfonic acid. Treatment of sulfate ester 23 with NaOH then led to aziridine 24. ... 

An old approach to preparing hydrocarbons such as 246 and 249 consists in the cycloaddition of ethenylidene carbenes to olefins [104]. In a recent application, such a carbene, 251, was generated from the dichloride 250 by n-butyllithium treatment trapping with 2,3-dimethyl-2-butene then led to the permethylated hydrocarbon 252 in 40% yield [103]. 

The preparation described here of 3-cyclopentene-1-carboxylic acid from dimethyl malonate and cis-1,4-dichloro-2-butene is an optimized version of a method reported earlier3 for obtaining this often used and versatile building block.6 The procedure is simple and efficient and requires only standard laboratory equipment. 3-Cyclopentene-1-carboxylic acid has previously been prepared through reaction of diethyl malonate with cis-1,4-dichloro(or dibromo)-2-butene in the presence of ethanolic sodium ethoxide, followed by hydrolysis of the isolated diethyl 3-cyclopentene-1,1-dicarboxylate intermediate, fractional recrystallization of the resultant diacid to remove the unwanted vinylcyclopropyl isomer, and finally decarboxylation.2>7 Alternatively, this compound can be obtained from the vinylcyclopropyl isomer (prepared from diethyl malonate and trans-1,4-dichloro-2-butene)8 or from cyclopentadiene9 or cyclopentene.10 In comparison with the present procedure, however, all these methods suffer from poor selectivity, low yields, length, or need of special equipment or reagents, if not a combination of these drawbacks. 

Volume 75 concludes with six procedures for the preparation of valuable building blocks. The first, 6,7-DIHYDROCYCLOPENTA-l,3-DIOXIN-5(4H)-ONE, serves as an effective /3-keto vinyl cation equivalent when subjected to reductive and alkylative 1,3-carbonyl transpositions. 3-CYCLOPENTENE-l-CARBOXYLIC ACID, the second procedure in this series, is prepared via the reaction of dimethyl malonate and cis-l,4-dichloro-2-butene, followed by hydrolysis and decarboxylation. The use of tetrahaloarenes as diaryne equivalents for the potential construction of molecular belts, collars, and strips is demonstrated with the preparation of anti- and syn-l,4,5,8-TETRAHYDROANTHRACENE 1,4 5,8-DIEPOXIDES. Also of potential interest to the organic materials community is 8,8-DICYANOHEPTAFULVENE, prepared by the condensation of cycloheptatrienylium tetrafluoroborate with bromomalononitrile. The preparation of 2-PHENYL-l-PYRROLINE, an important heterocycle for the synthesis of a variety of alkaloids and pyrroloisoquinoline antidepressants, illustrates the utility of the inexpensive N-vinylpyrrolidin-2-one as an effective 3-aminopropyl carbanion equivalent. The final preparation in Volume 75, cis-4a(S), 8a(R)-PERHYDRO-6(2H)-ISOQUINOLINONES, il lustrates the conversion of quinine via oxidative degradation to meroquinene esters that are subsequently cyclized to N-acylated cis-perhydroisoquinolones and as such represent attractive building blocks now readily available in the pool of chiral substrates. 

The condensation of the cinnamaldehyde derivative (18) with ethoxycarbonyl-pentyltriphenylphosphorane in DMF gave a mixture of tram-trans- and trans-cis-products.22 A general method to prepare l-substituted-m-9-alkenes (19), using a stereoselective Wittig reaction, has been described.23 2,2-Dimethyl-3-butenal (20)... 

The ozonolysis reaction, followed by reductive workup with sulfur dioxide, as described in Part A of the present procedure, illustrates a general method which has been developed for the preparation of acetals. Application of the procedure is illustrated by conversion of the following olefins in alcoholic solution to the corresponding acetals (1) l-chloro-4-(o-nitrophenyl)-2-butene to o-nitrophenylacetaldehyde dimethyl acetal in 84% yield (2) l,4-dibromo-2-butene tobromoacetaldehyde dimethyl acetal in 67% yield (3) 3-butenoic acid to malonaldehydic acid diethyl acetal ethyl ester in 61% yield (4) cyclopentadiene to malonaldehyde bis(diethyl acetal) in 48% yield and (5)... 

Di-/i-chloro-bis(7)4-1,5-cyclooctadiene)dirhodium(l), [RhCl(l,5-C8Hi2)]2, has been prepared in 60% yield by reducing rhodium trichloride hydrate in the presence of excess olefin in aqueous ethanol.1 In the present preparation the yield has been greatly increased (to 94%). Two related complexes, [RhCl(l,5-C6Hio)]22 and [RhCl(C6H12)2]2, are similarly prepared in high yield from 1,5-hexadiene and 2,3-dimethyl-2-butene, respectively. 

The new 2,3-dimethyl-2-butene complex, [RhCl(C6H12)2]2, is prepared by a similar method, in which the solution is left at 20° for 30 days instead of being refluxed. A trace of metallic rhodium is deposited. This is removed by recrystallization from dichloromethane-diethyl ether to give an analytically pure product yield 75%. 

Expecting that the introduction of 1,2-dimethyl substituents to ( )-cycIoalkenes should increase non-bonding interaction across the ring, Marshall and coworkers 29) prepared (—)-( )-l,2-dimethylcyclodecene (27a) and showed that this compound is optically quite stable. In their synthetic approach to 27a, they started from the p-keto ester 24 which was converted into (+)-25 through a sequence of reactions involving condensation with 3-buten-2-one, LiAlH reduction, and resolution via the camphor-... 

Chlorothexylborane (1). Mol. wt. 132.44. One synthesis involves the reaction of thexylborane with 1 equivalent of hydrogen chloride in ether.1 This reagent can also be prepared by reaction of 2,3-dimethyl-2-butene with monochloroborane -dimethyl sulfide (equation I).2... 

This procedure describes the preparation of 3-nitropropanai, 1, employing the rarely encountered 1,4-addition of ambident nitrite ion with its "softer N-atom,2 and further transformations of 1, as reported earlier.3 A similar preparation of 3-nitrobutanal from crotonaldehyde (3-butenal) is known,4 as well as analogous additions to a, 3-enones.2 The reduction of 1 to the alcohol 2, originally carried out with borane-dimethyl sulfide (BMS),3 is now more conveniently and economically done with sodium borohydride. The acetalization of 1 to yield the dimethyl acetal 3 is based on our earlier report.3... 

The borane is prepared through the addition of B2H6 to 2,3-dimethyl-2-butene and, because of steric hindrance, only the monoalkylborane is formed (Section 11-6 A) ... 

When PhMn(CO)s reacts with trans-1,3-pentadiene, and the resulting acyl substituted derivative 68 heated to 120°C (0.1 mm Hg), loss of carbon monoxide leads to a 73% yields of 69 [Eq. (32)] (226). Recently a derivative 70 of the parent ligand has been prepared from (Ph3P)2ReH7 and furan under reflux in thf, in the presence of 3,3 -dimethyl-1-butene as hydrogen acceptor (227). 

The intramolecular 13C isotope effects on the ene reaction with 102 oxygen were determined for 2,3-dimethyl-l-buten-3-ol 43 prepared from 2,3-dimethyl-but-2-ene 89... 

C. (E)-3,3-Dimethyl-l-phenyl-1 -butene. In a 1-L, two-necked, round-bottomed flask fitted with a reflux condenser, rubber septum, and a magnetic stirring bar are placed 17.8 g (0.08 mol) of 2-methyl-2-(2-phenylethenyl)-1,3-dithiolane and 2.17 g (0.004 mol) of [1,3-bis(diphenylphosphino)propane]nickel(ll) chloride [NiCl2(dppp)] (Note 5). The flask is evacuated and flushed with nitrogen three times. To the above mixture is added 300 mL of anhydrous tetrahydrofuran (Note 6). The ether solution of methylmagnesium iodide prepared in Step B is introduced with a double-ended needle in one portion (Note 7). The mixture is heated under reflux for 24 hr, cooled to room temperature, and treated with 200 mL of saturated ammonium chloride solution. 

Thexylchloroborane-Dimethyl sulHde (1). This boranc can be prepared by treating thexylborane-dimethyl sulfide with hydrogen chloride or by hydroboration of 2,3-di-methyl-2-butene with monochloroborane-dimethyl sulfide. 

Stereospecific synthesis of (2Z,4E,6E)-3,7,11-trimethyl-2,4,6,10-dodecatetraene, trans (Cio)-allofamesene 49), isolated from Perilla fmtscem Makino, was realized by the ptdladium-catalyzed cross-coupling of 4,8-dimethyl-l,3,7-nonatrienyl-l,3,2-benzodioxaborole 48) with (Z)-2-bromo-2-butene. The benzodioxaborole derivative 48) was prepared by hydroboration of 4,8-dimethylnona-3,7-dien-l-yne 47), obtained via two steps from geranial, with 1,3,2-benzodioxaborole (Eq- 112) Bombykol and its geometrical isomers were also synthesized selectively... 

When each stereoisomeric reactant forms a different stereoisomeric product the reaction is known as stereospecific reaction. For example, the addition of CBr2 (dibromo-carbene, prepared from bromoform and base) to ds-2-butene gives cis-2,3-dimethyl-l,l-dibromocyclopropane (1.32), whereas addition of CBr2 to the trans-isomer exclusively yields the trans-cyclopropane 1.33. 

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