2-Methylbut-2-ene

Tietze et al. investigated the Diels-Alder reaction between 44 and 2-methylbut-2-ene at the B3-LYP/6-31G level (Scheme 30) [98EJ02733]. 

In the next step, one of the borane-hydrogens is transferred to a sp -carbon center of the alkene and a carbon-boron bond is formed, via a four-membered cyclic transition state 6. A mono-alkyIborane R-BH2 molecule thus formed can react the same way with two other alkene molecules, to yield a trialkylborane R3B. In case of tri- and tctra-substituted alkenes—e.g. 2-methylbut-2-ene 7 and 2,3-dimethylbut-2-ene 9—which lead to sterically demanding alkyl-substituents at the boron center, borane will react with only two or even only one equivalent of alkene, to yield a alkylborane or mono alky Iborane respectively ... 

PTAD spontaneously reacts with various olefins to give the corresponding ene adducts, for example, the reaction with 2-methylbut-2-ene gives a nearly quantitative yield of 645 <1980JOC3467>. When the reaction is run in acetone in the presence of various salts, for example, magnesium perchlorate, in addition to 645, triazolol l, 2-r oxadiazine 646 is formed in 10-30% yield, depending on the reaction conditions (Scheme 105) <1994T1821>. 

If we consider protonation of 2-methylbut-2-ene, then two different carbocations might be formed. One of these is tertiary, and thus favourable, because three electron-donating alkyl groups help to stabilize the cation by dispersing the charge (see Section 6.2.1). The alternative carbocation intermediate is less favourable, in that it is secondary, with just two alkyl... 

Fig. 4. Different possible conformations of cw-l,4-polyisoprene (poly[(Z)-2-methylbut-2-ene-l,4-diyl]) in the crystalline state, as viewed sideways along two orthogonal axes [17].

Marston, G., C. D. McGill, and A. R. Rickard, Hydroxyl-Radical Formation in the Gas-Phase Ozonolysis of 2-Methylbut-2-ene, Geophys. Res. Lett, 25, 2177-2180 (1998). 

The hydrofluorination of alkenes with anhydrous hydrogen fluoride has been already described extensively in Houben-Weyl, Vol. 5/3, pp 100-101. In the case of ethene, the yield of fluoroethane increases on raising the temperature (90°C, 20-25 atm), however, the procedure should be carried out at lower temperatures with higher alkenes because of their tendency to polymerize thus, 2-fluoropropane is formed in 60-75% yield at 0-45 C. Similar procedures have been described for 2-fluorobutane, 2-fluoro-2-methylpropane and 2-fluoro-2-methyl-butane from but-l-ene, 2-methylpropene and 2-methylbut-2-ene, respectively.63 Cyclohexene reacts at — 78 C with hydrogen fluoride to give fluorocyclohexane (70%) at 100 C polymerization is observed.59,60 Two equivalents of hydrogen fluoride to allene are taken up at — 70 C, to form 2,2-difluoropropane (50%).64... 

Pentafluorocthyl iodide is of practical interest, particularly as a precursor of higher perfluoroal-kyl iodides. There are several patents for the preparation of the key compound from tetra-fluoroethene, iodine pentafluoride and iodine at 75-80 C in the presence of catalysts anti-mony(III) fluoride, titanium(lV) chloride, boron trifluoride, vanadium(V) fluoride, niobium(V) fluoride, and molybdenum(Vl) fluoride.11-13 The agents iodine monofluoride" and bromine monofluoride" can add to branched pcrfluoroalkcnes, e.g. perfluoro-2-methylbut-2-ene gives perfluoro-2-iodo-2-methylbutane.1415... 

A soln of the crude aldehyde (76.3 mg, 0.38 mmol) in tBuOH (2mL) and phosphate buffer (2mL, 1M, pH 4) was treated with 2-methylbut-2-ene (0.1 mL, 0.94 mmol) and NaC102 (36 mg, 0.40 mmol), and was stirred at rt for 30 min. The mixture was extracted (CHC13, 10x5mL) and the combined organic layers were dried (Na2SQ4) to yield crude 152 as a yellow viscous liquid yield 74 mg (87%). 

When the reaction is applied to an unsymmetrically substituted alkene, the major photoproduct or products are those arising from the most stable diradical intermediate. This is illustrated in the irradiation of benzaldehyde in 2-methylbut-2-ene in which the principal products are the stereoisomeric oxetanes arising from the same diradical intermediate [Eq. (70)].278 The oxetanes resulting from addition in the alternative sense [Eq. (71)] are minor products, as are other products arising by allylic hydrogen abstraction. 

The relative rates of insertion into the OH bond of methanol and addition to 2-methylbut-2-ene indicate that the jS-thiophosphinoylcarbene (59) has enhanced nucleophilicity.66 This was interpreted as being due to hyperconjugative electron... 

The majority of mono- and di-substituted alkenes undergo hydroboration to give trialkylboranes which are then available for a variety of synthetic procedures. With some alkenes, alkylation of borane does not go to completion and the resulting mono- or di-alkyl boranes are useful in synthesis as modified boranes. Thus, 2-methylbut-2-ene gives bis(3-methyl-2-butyl)borane (idisiamylborane). 

This borane reagent may be prepared as follows.6 In a dry 500-ml flask equipped with a condenser, a thermometer and a pressure-equalising dropping funnel are placed 80 ml of diglyme, 23.1 g of 2-methylbut-2-ene (0.33 mol) in 20ml of diglyme and 4.7 g of sodium borohydride (0.125 mol). The flask is immersed in an ice bath and 23.5 g of boron trifluoride-etherate (0.165 mol) is added dropwise over a period of 30 minutes. The semi-solid reaction mixture containing 0.165 mol of disiamylborane is permitted to remain an additional 15 hours at 0-5 °C, and then used for hydroboration. Examples of the use of disiamylborane are described in Sections 5.4.3 p. 542 and 5.7.1, p. 588. 

The method is illustrated by the conversion of 2-methylbut-2-ene (Expt 5.12) into 2-methylbutane (Expt 5.1). The experiment has been incorporated to illustrate the handling of low boiling point liquids, and also to illustrate some aspects of interpretative infrared spectroscopy. 

In the preparative example of the dehydration of 2-methylbutan-2-ol [Me2C(OH)-CH2-Me], the loss of a proton from the intermediate carbocation (2) may take place from either of the two adjacent positions giving a mixture of regioisomers, 2-methylbut-2-ene (3) and 2-methylbut-l-ene (1) (Expt 5.12). 

The first examples of ortho cycloaddition can be found in a U.S. patent of Ayer and Buchi [1], Benzonitrile and 2-methylbut-2-ene are reported to yield 7,8,8-trimethylbicyclo[4.2.0]octa-2,4-diene-l-carbonitrile upon irradiation under nitrogen with a mercury resonance arc. Similar reactions, all leading to derivatives of bicyclo[4.2.0]octa-2,4-diene-l-carbonitrile occurred when benzonitrile was irradiated in the presence of 2,4,4-trimethylpent-l-ene, ethyl vinyl ether, vinyl acetate, methyl vinyl ketone, and methyl acrylate. The addend pairs para-tolunitrile/oct-l-ene, ort/m-dicyanobenzene/2-methylbut-2-ene, para-dicyanobenzene/but-l-ene, 2,3-dimethylbenzonitrile/propene, and 3,4,5-trimethylbenzonitrile/ethene likewise produced ortho photocycloadducts. 

In one of the earliest reports on ortho photocycloaddition, in which the reaction of benzonitrile with 2-methylbut-2-ene is described, a diradical (triplet) intermediate was proposed [73], The structure of the product corresponds to the most stable of the four possible diradical intermediates. When benzophenone was added as a sensitizer in an attempt to increase the yield of the photoadduct, only 0.05% of ortho adduct was isolated along with 54% of an oxetane formed by the addition of benzophenone to 2-methylbut-2-ene. In the absence of benzophenone, the ortho adduct was isolated in 63% yield. It is, however, thermally as well as photochemically unstable and reverts to starting materials, supposedly also via a biradical. The authors propose that benzophenone catalyzes bond cleavage of the adduct more efficiently than ortho addition and this would account for the low yield of photoadduct in the presence of benzophenone. From these experiments, no conclusion about the identity of the reactive excited state can be drawn. 

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