F 2-Butenal

FIGURE 7.13 Anti addition of Br2to (f)-2-butene gives meso-2,3-dibromobu-tane. 

The numbers in brackets for propylene, isobutylene, f-2-butene and 1,3-butadiene entries are at the QCISD(T)//QCISD/6-31G(d) level of theory CBS-Q//QCISD/6-31G(d) gas-phase inhinsic barriers (A ) for the epoxidation of -2-butene with dimethyldioxirane (DMDO) and peroxyformic acid are 9.7 and 11.2 kcal moL, respectively. 

FIGURE 19. B3LYP/6-31 l+G(d,p)-optimized transition structures for the epoxidation of cyclohexene with DMDO in the presence of one (a) and two (b) water molecules. The transition structure for the epoxidation of F-2-butene (c) is optimized at the same level of theory in the presence of one water molecule. The classical barriers are estimated using total electronic energies of the transition structures, cyclohexene (—234.71316 au), -2-butene (-157.27453 au), DMDO with one water molecule (—344.81523 au) and DMDO with two water molecules (—421.28672 au)... 

Butylenes can be catalytically hydrogenated in the presence of Pt, Pd, or Ni in an exothermic reaction. In the absence of a catalyst, this reaction proceeds at a negligible rate, even at elevated temperatures. Heats of hydrogenation in kj/mol are as follows 1-butene, —126.8 isobutylene, —118.8 Of-2-butene, —119.7 and tran,f-2-butene, -115.5. 

Internal polyfluoroalkenes are less reactive toward S03. Indeed, fluorosulfate was obtained in low yield in reaction of F-2-butene and S03 and BF3 at 150°C [175]. However, much better results were achieved when a stronger Lewis acid was employed. Interaction of internal F-olefins with S03 stabilized by antimony pentafluoride proceeds at 75-80°C resulting in the corresponding fluorosulfates 89a-e [178,179] ... 

The nature of the halogen bonded to the sulfenyl sulfur atom does not affect the stereochemical course of the addition. For example, the reaction of 2,4-dinitrobenzenesulfenyl bromide with (Z)- and (F )-2-butenes gives the products 4 of anfz-stereoselective addition168. 

When bromine adds to (Z)- or (f )-2-butene, the product 2,3-dibromobutane contains two equivalently substituted stereogenic centers ... 

Direct photochemical excitation of unconjugated alkenes requires light with < 220nm. A study of Z- and F-2-butene diluted with neopentane demonstrated that cis-trans isomerization was competitive with the photochemical [2tt + 2tt]... 

Figure 7.7 Enthalpy profile of the reaction of f-2-butene (bottom) with the second-generation Grubbs benzylidene cataiyst to give p-methylstyrene. Solid lines depict the bottom-bound pathway (trans-chlorides), while the dotted lines depict the side-bound pathway (c/s-chlorides). Calculated at the M06/LACV3P-H- (2f)//B3LYP/l ACVP level of theory (with single-point solvent corrections in CH2CI2). Adapted from Ref. [15].

Figure 7.20 3D structures of transition states leading to Z- and f-2-butene products in the homodimerization of propene catalyzed by an adamantyl-chelated ruthenium catalyst. 

Scheme 6.16. Representations of the course of electrophilic addition of bromine (Br2) to cis- or (Z)- and trans- or f )-2-butene to give, respectively, racemic or (+)-2,3-dibromobutane and mejo-2,3-dibromobutane.

Explain the following facts Treating (Z)-2-butene with OSO4 in pyridine and then NaHSOs in water gives a diol that is optically inactive and cannot be resolved. Treating (f )-2-butene with the same reagents gives a diol that is optically inactive but can be resolved into enantiomers. 

STRATEGY AND ANSWER Recall that the reaction in either instance results in syn hydroxylation of the double bond of each compound. Syn hydroxylation of (f )-2-butene gives a pair of enantiomers, while syn hydroxylation of (Z)-2-butene gives a single product that is a meso compound. 

The ene reaction of the activated imino-group in (199) with olefins provides an effective synthesis of the adducts (200), which are converted into y,S-unsaturated-a-amino-acids (Scheme 91). It has also been reported that the ene reaction between a-bromoacrylate and f-2-butene, catalysed by EtAlCl2,... 

---