Double 1,2-disubstituted

Synthesis All by standard steps. Though the Michael addition on A could in the ciy occur at either double bond, the unsubstituted position out of the ring is much more reactive than the disubstituted position in the ring and only the wanted reaction occurs. Bull. Soc. Chim. France. 1955, 8. 

Conventional synthetic schemes to produce 1,6-disubstituted products, e.g. reaction of a - with d -synthons, are largely unsuccessful. An exception is the following reaction, which provides a useful alternative when Michael type additions fail, e. g., at angular or other tertiary carbon atoms. In such cases the addition of allylsilanes catalyzed by titanium tetrachloride, the Sakurai reaction, is most appropriate (A. Hosomi, 1977). Isomerization of the double bond with bis(benzonitrile-N)dichloropalladium gives the y-double bond in excellent yield. Subsequent ozonolysis provides a pathway to 1,4-dicarbonyl compounds. Thus 1,6-, 1,5- and 1,4-difunctional compounds are accessible by this reaction. 

A interesting and useful reaetion is the intramolecular polycyclization reaction of polyalkenes by tandem or domino insertions of alkenes to give polycyclic compounds[l 38]. In the tandem cyclization. an intermediate in many cases is a neopentylpalladium formed by the insertion of 1,1-disubstituted alkenes, which has no possibility of /3-elimination. The key step in the total synthesis of scopadulcic acid is the Pd-catalyzed construction of the tricyclic system 202 containing the bicyclo[3.2. Ijoctane substructure. The single tricyclic product 202 was obtained in 82% yield from 201 [20,164). The benzyl chloride 203 undergoes oxidative addition and alkene insertion. Formation of the spiro compound 204 by the intramolecular double insertion of alkenes is an exam-ple[165]. 

For 2,4- or 4,5-disubstituted derivatives, there is a double coupling between the ttij and i>(C2X) or viC X) vibration on one hand and oscillations a)(, and n(C4X) on the other. These interactions induce, for the first one, two frequencies either higher (suite V) or lower (suite VIII), for the second, two other frequencies either higher (suite VI) or lower (suite VlII). 

Degree of substitution We classify double bonds as monosubstituted, disubstituted,... 

The major product is 2 3 dimethyl 2 butene It has a tetrasubstituted double bond and IS more stable than 2 3 dimethyl 1 butene which has a disubstituted double bond The major alkene arises by loss of a hydrogen from the p carbon that has fewer attached hydrogens (C 3) rather than from the p carbon that has the greater number of hydrogens (C 1) ... 

Water may remove a proton from either Cl or C 3 of this carbocation Loss of a proton from C 1 yields the minor product 2 3 dimethyl 1 butene (This alkene has a disubstituted double bond )... 

Hydrocarbons that contain a carbon-carbon triple bond are called alkynes Non cyclic alkynes have the molecular formula C H2 -2 Acetylene (HC=CH) is the simplest alkyne We call compounds that have their triple bond at the end of a carbon chain (RC=CH) monosubstituted or terminal alkynes Disubstituted alkynes (RC=CR ) have internal triple bonds You will see m this chapter that a carbon-carbon triple bond is a functional group reacting with many of the same reagents that react with the double bonds of alkenes... 

The carbonyl carbon of a ketone bears two electron releasing alkyl groups an aldehyde carbonyl group has only one Just as a disubstituted double bond m an alkene is more stable than a monosubstituted double bond a ketone carbonyl is more stable than an aldehyde carbonyl We 11 see later m this chapter that structural effects on the relative stability of carbonyl groups m aldehydes and ketones are an important factor m then rel ative reactivity... 

Dibromoborane—dimethyl sulfide is a more convenient reagent. It reacts directly with alkenes and alkynes to give the corresponding alkyl- and alkenyldibromoboranes (120—123). Dibromoborane differentiates between alkenes and alkynes hydroborating internal alkynes preferentially to terminal double and triple bonds (123). Unlike other substituted boranes it is more reactive toward 1,1-disubstituted than monosubstituted alkenes (124). 

Among chiral dialkylboranes, diisopinocampheylborane (8) is the most important and best-studied asymmetric hydroborating agent. It is obtained in both enantiomeric forms from naturally occurring a-pinene. Several procedures for its synthesis have been developed (151—153). The most convenient one, providing product of essentially 100% ee, involves the hydroboration of a-pinene with borane—dimethyl sulfide in tetrahydrofuran (154). Other chiral dialkylboranes derived from terpenes, eg, 2- and 3-carene (155), limonene (156), and longifolene (157,158), can also be prepared by controlled hydroboration. A more tedious approach to chiral dialkylboranes is based on the resolution of racemates. /n j -2,5-Dimethylborolane, which shows excellent enantioselectivity in the hydroboration of all principal classes of prochiral alkenes except 1,1-disubstituted terminal double bonds, has been... 

The 1,1-disubstitution of chlorine atoms causes steric interactions in the polymer, as is evident from the heat of polymeri2ation (see Table 1) (24). When corrected for the heat of fusion, it is significantly less than the theoretical value of —83.7 kJ/mol (—20 kcal/mol) for the process of converting a double bond to two single bonds. The steric strain apparentiy is not important in the addition step, because VDC polymeri2es easily. Nor is it sufficient to favor depolymeri2ation the estimated ceiling temperature for poly (vinyhdene chloride) (PVDC) is about 400°C. 

Reductions of avemiectin containing five double bonds with Pd oi Pt catalysts proceed at almost comparable rates at the two disubstituted 10,11- and... 

The widespread use of cinnamic derivatives has led to the pursuit of reUable methods for thek dkect synthesis. Commercial processes have focused on condensation reactions between ben2aldehyde and a number of active methylene compounds for assembly of the requisite carbon skeleton. The presence of a disubstituted carbon—carbon double bond in the sidechain of these chemicals also gives rise to the existence of two distinct stereoisomers, the cis or (Z)- and trans or (E)- isomers ... 

Disubstituted pyridazine-3,6(l//,2//)-diones add halogens to the 4,5-double bond, followed by dehydrohalogenation to give 4-halo derivatives. 1,2-Disubstituted 5-bromopyridazine-3,6(l//,2F0 diones react with bromine to give the corresponding 4,5-dibromo derivative. The Mannich reaction with 2-arylpyridazin-3(2//)-one occurs at position 4. 

In the alternative approach.the 1,3-dipolar system can be constructed in several ways. Treatment of a-chloroacylhydrazones of diaryl ketones and certain aralkyl and dialkyl ketones (382) with NaH in anhydrous THF gives l-(disubstituted methylene)-3-oxo-l,2-diazetidinium inner salts (383). Reaction of (383) with DMAD in methylene chloride gave (384), a 2 1 adduct with loss of CO. Double bond migration in (384) occurred on heating to give (385). The intermediate in the cycloaddition was found to be (386), which on heating lost CO to form a new ylide system which in turn underwent reaction with more DMAD <81JA7743). 

Protons of substrueture B and C are assigned by means of the mesomerie effeet of the aldehyde group whieh deshields the protons in o-position of the attaehed p-disubstituted benzenoid ring and in p-position of the eentral CC double bond ort/io-protons of the monosubstituted benzenoid ring D split into a doublet beeause of one ortho eoupling ( 7.5 Hz) while the meta-protons split into a triplet beeause of two ortho eouplings. 

Ozone cracking is a physicochemical phenomenon. Ozone attack on olefinic double bonds causes chain scission and the formation of decomposition products. The first step in the reaction is the formation of a relatively unstable primary ozonide, which cleaves to an aldehyde or ketone and a carbonyl. Subsequent recombination of the aldehyde and the carbonyl groups produces a second ozonide [58]. Cross-linking products may also be formed, especially with rubbers containing disubstituted carbon-carbon double bonds (e.g. butyl rubber, styrene-butadiene rubber), due to the attack of the carbonyl groups (produced by cleavage of primary ozonides) on the rubber carbon-carbon double bonds. 

The hydroboration step, being very sensitive to steric effects, yields only secondary alkylboranes from trisubstituted double bonds, whereas the less hindered alkylborane is formed predominantly from disubstituted steroidal double bonds. The diborane attack occurs usually towards the a-side and hence results in overall a-hydration of double bonds after alkaline hydrogen peroxide oxidation. ... 

Degree of substitution. We classify double bonds as monosubstituted, disubstituted, trisubstituted, or tetrasubstituted according to the number of carbon atoms directly attached to the C=C stnactural unit. 

Monosubstituted alkenes (RCH=CH2) have a more stabilized double bond than ethylene (unsubstituted) but are less stable than disubstituted alkenes. 

Disubstituted alkene (Section 5.6) Alkene of the type R2C=CH2 orRCH=CHR. The groups R may be the same or different, they may be any length, and they may be branched or unbranched. The signihcant point is that there are two carbons directly bonded to the carbons of the double bond. 

In fact, esters of amino alcohols and 2,2-disubstituted plii iiylacetic acids show useful antitussive activity the mecha-lM iii of action may include bronchiodilation. Double alkylation III the anion of phenylacetonitrile with 1,4-dibromobutane gives llit i cyclopentane-substituted derivative (33). Saponification... 

Since bond rotation can t occur, the two 2-butenes can t spontaneously interconveTt they are different, isolable compounds. As with disubstituted cycloalkanes, we call such compounds cis-trans stereoisomers. The compound with substituents on the same side of the double bond is called c/3-2-butene, and the isomer with substituents on opposite sides is fra/iS-2-butene (Figure 6.3). 

Methyl-2-hexcne has a disubstituted double bond, RCH=CHR, and would probably give a mixture of two alcohols with either hydration method since Markovnikov s rule does not apply to symmetrically substituted alkenes. 3-MethyI-3-hexene, however, has a trisubstituted double bond, and would give only the desired product on non-Markovnikov hydration using the hydroboration/oxidation method. 

If dichlorocarbene is generated in the presence of an alkene, addition to the double bond occurs and a dichlorocyclopropane is formed. As the reaction of dichlorocarbene with ds-2-pentene demonstrates, the addition is stereospecific, meaning that only a single stereoisomer is formed as product. Starting from a cis alkene, for instance, only cis-disubstituted cyclopropane is produced starting from a trans alkene, only trans-disubstituted cyclopropane is produced. 

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