Olefins multisubstituted

Hydroamination of olefins under most catalytic conditions proceed with Markovnikov addition of the N-H bond across the olefin. Shown below is a rhodium-catalyzed intramolecular, anti-Markovnikov, hydroamination developed for the synthesis of 3-arylpiperidines 167 <06JA6042>. Further evaluation of this reaction as a synthesis of multisubstituted piperidines revealed that substrates with substituents a or y to the amino group did not produce the expected piperidine, however, substrates with a substituent (1 to the amino group produce piperidines in high yield. 

Although various transition-metal complexes have reportedly been active catalysts for the migration of inner double bonds to terminal ones in functionalized allylic systems (Eq. 3.2) [5], prochiral allylic compounds with a multisubstituted olefin (Rl, R2 H in eq 2) are not always susceptible to catalysis or they show only a low reactivity [Id]. Choosing allylamines 1 and 2 as the substrates for enantioselective isomerization has its merits (1) optically pure citronellal, which is an important starting material for optically active terpenoids such as (-)-menthol, cannot be obtained directly from natural sources [6], and (2) both ( )-allylamine 1 and (Z)-allylamine 2 can be prepared in reasonable yields from myrcene or isoprene, respectively, The ( )-allylamine 1 is obtained from the reaction of myrcene and diethylamine in the presence of lithium diethylamide under Ar in an almost quantitative yield (Eq. 3.3) [7], The (Z)-allylamine 2 can also be prepared with high selectivity (-90%) by Li-catalyzed telomerization of isoprene using diethylamine as a telomer (Eq. 3.4) [8], Thus, natural or petroleum resources can be selected. 

Friedel Crafts type alkylations of benzene by alkenes involve the initial formation of a lattice associated carbenium ion, formed by protonation of the sorbed olefin. The chemisorbed alkene is covalently bound to the zeolite in the form of an alkoxy group and the carbenium ion formed exists only in the transition state. As would be expected fixjm conventional Friedel Crafts alkylation, the reaction rate over acidic molecular sieves also increases with the degree of substitution of the aromatic ring (tetramethyl > trimethyl > dimethyl > methyl > unsubstituted benzene). The spatial restrictions induced by the pore size and geometry frequently inhibit the formation of large multisubstituted products (see also the section on shape selectivity). 

Multisubstituted olefins (including those with heterocyclic substituents), their synthesis and applications to materials science and pharmaceutical chemistry 06BCJ811. 

This reaction has general application in the synthesis of multisubstituted olefins. 

A more sophisticated case is the series of reactions using 2-pyridyldimethyl(vinyl)silane as platform for the synthesis of multisubstituted olefins. The general approach is sketched in Scheme 20, although different combinations of the methods can be used. The purpose of the SiMc2py group is to benefit from the so-called... 

Desulfurization of the multisubstituted allylsulfides 78 and 80 results in isomerization of the olefin to give the less substituted one 79, probably due to the steric strain in the transition states of the protonation of the ally he radical or anion species (Fig. 26). 

The importance of the torquoselective olefination is illustrated in Fig. 34 for the particular case in which a multisubstituted alkenylsilane is converted to various kinds of multisubstituted olefins. The silyl-substituted allyl alcohol 93 is allylated to give the 1,4-diene 94, and the iodoalkene 95, prepared by desilyliodination of 93, is subjected to palladium-catalyzed cross-coupling reactions (the Heck reaction, Stille coupling) to afford the dienes 96 and 97 without ElZ isomerization. 

Fig. 34 Various conversions of alkenylsilanes into multisubstituted olefins...

Although various transition-metal complexes have reportedly been active catalysts for the migration of inner double bonds to terminal ones in functionalized allylic systems (Eq. 3.2) [5], prochiral allylic conqwunds with a multisubstituted olefin (R , H in eq 2) are not always... 

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