Alkenes, with acids compounds

Reaction of alkenes with carbonyl compounds or carbonyl derivatives in the presence of Lewis acids, the ene reaction, enables the stereoselective preparation of highly functionalized compounds. Copper Lewis acids activate both aldehydes and imines in ene reactions. Evans has reported that Cu(II) Lewis acids catalyze glyoxylates in reactions with alkenes (Sch. 56) [103]. The homoallylic alcohols 257 and 259 are produced in high yield and enantioselectivity. The bis aquo complex 260 is a readily prepared and air-stable catalyst and gave high chemical yield and excellent selectivity in the ene reactions. Another point of note is that catalysts 260 and 261 furnish enantiomeric products even though they differ from each other only by the substituent at the 4-posi-tion of the oxazoline. 

Charette et al. examined a Rh(ll)-carboxylate catalyst with four amino acid derived M-phthaloyl ligands [129]. This catalyst has seen widespread use, for example in the cyclopropanation of alkenes with diazo compounds. Depending on the orientation of these ligands (up or down), four different symmetries are possible. Previous studies were unable to clarify which is the enantioselectively active one (Scheme 15). 

Low -molecular-weight ozonides are explosive and are theretore not isolated. Instead, the ozonide is immediately treated with a reducing agent such as zinc metal in acetic acid to convert it to carbonyl compounds. The net result of the ozonolysis/reduction sequence is that the C=C bond is cleaved and oxygen becomes doubly bonded to each of the original alkene carbons. If an alkene with a letrasubstituted double bond is ozonized, two ketone fragments result if an alkene with a trisubstituted double bond is ozonized, one ketone and one aldehyde result and so on. 

We have investigated the bromo-addition of alkenes and their related compounds with BTMA Br3. Thus, we found that the reaction of alkenes with BTMA Br3 in aprotic solvents such as dichloromethane and chloroform gave 1,2-dibromo adducts in a manner of stereospecific anti-addition, and, in such protic solvents as methanol and acetic acid, gave the corresponding dibromo adducts along with considerable amounts of solvent-incorporated products in regioselective manner (Fig. 18) (ref. 29). 

Trialkylsilyl groups have a modest stabilizing effect on adjacent carbanions (see Part A, Section 3.4.2). Reaction of the carbanions with carbonyl compounds gives (3-hydroxyalkylsilanes. (3-Hydroxyalkylsilanes are converted to alkenes by either acid or base.270 These eliminations provide the basis for a synthesis of alkenes. The reaction is sometimes called the Peterson reaction.211 For example, the Grignard reagent derived from chloromethyltrimethylsilane adds to an aldehyde or ketone and the intermediate can be converted to a terminal alkene by acid or base.272... 

Relevant complexes have been isolated and fully characterized (4-10, 13-lb). The resulting arylpalladium complex 8 is able to react with various compounds such as terminal alkenes, alkynes, aryl boronic acids or hydrogen-transfer agents to give an organic molecule and palladium(O) (3, 17, 18). 

Alkenes with a 1,1-disubstitution pattern form tertiary carbocations upon treatment with a Brpnsted acid. Consequently, such compounds are often easily reduced (Eq. 72). An example of this is the formation of 2-methylpentane in 93% yield after only 5 minutes when a dichloromethane solution of 2-methyl-1-pentene and 1.4 equivalents of triethylsilane is treated with 1.4 equivalents of trifluoromethanesulfonic acid at —75°.216 Similar treatment of 2,3-dimethyl-l-butene gives a 96% yield of 2,3-dimethylbutane.216... 

Trisubstituted Alkenes. With very few exceptions, trisubstituted alkenes that are exposed to Brpnsted acids and organosilicon hydrides rapidly undergo ionic hydrogenations to give reduced products in high yields. This is best illustrated by the broad variety of reaction conditions under which the benchmark compound 1-methylcyclohexene is reduced to methylcyclohexane.134 146,192 202 203 207-210 214 234 When 1-methylcyclohexene is reduced with one equivalent of deuterated triethylsilane and two equivalents of trifluoroacetic acid at 50°, methylcyclohexane-... 

Negishi previously reported that a wide variety of Lewis-acidic compounds catalyzed hydrozirconation of alkenes such as 1-decene 108 with /-BuZrCp2Cl.126 It was found that the reaction of 1-decene with 1.1 molar equiv. of TIB A, in the presence of 2-5 mol% of chlorine-containing late transition metals, led to the formation of 1-iododecane 110 after treatment of the product with iodine (Table 9). 

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