Tranj-selective reaction

Optically active catalyst 1 can be obtained either by enantiomer-selective reaction of rac.-2 with optically active lithium (l,l -binaphthyl)-2,2 -diolate or by direct resolution by chiral HPLC. Optically active 21 and 22 in addition to 1 were successfully obtained by HPLC resolution and used for the polymerization of 1,5-hexadiene [60-62], Both catalysts gave an optically active polymer through cyclopolymerization. The optical activity and the content of tranj-structure in the main chain of the polymers obtained with 21 and 22 were comparable with those of the polymers synthesized with 1 [61,62],... 

The photo-cycloaddition of alkenes and dienes to styrenes and stilbenes has been recently reviewed by Lewis (1979). tranj-Stilbene adds to many electron-rich alkenes to give [2 + 2]-cycloaddition products (Kaupp et al., 1978). Similar products are formed with vinylene carbonate (Lewis and Hoyle, 1977). Conjugated 1,3-dienes give [2 + 2]-cycloaddition products (Lewis and Hoyle, 1977 Lewis and Johnson, 1977). When nonpolar solvents are used, the reaction is modestly regioselective, but as the polarity of the solvent is increased the selectivity increases. Since the dienes quench the fluorescence of the stilbenes, it appears that exciplexes are involved. [2 + 2]-Cycloaddition takes place when indene (Sket and Zupan, 1976) and imidazoles (Ito and Matsura, 1979) are irradiated in the presence of hexafluorobenzene and... 

As noted in Section 2.2.2.3.2.1.1.1. seven-membered-ring products are obtained, as mixtures of CIS- and tranj-isomers, from the palladium(0)-catalyzed reaction of dimethyl ( , )-hexa-2,4-dienedioate (2) with MCP (i).i2a,66c, 119 nickel(0)/phosphite catalyst systems are employed, the selectivity for the formation of the [3 -I- 2] cycloadduct 3 increases. More interestingly, only cis-4 is formed in these cases. 

This model also predicts that selectivity for the rran -fused cycloadducts in nonatriene (n = 0) or deca-triene (n = 1) cyclizations should increase as size of the coefficients at C(2)/C(6 + n) are increased relative to those at C(l)/C(9 -i- n), that is, as the polarization of the dienophile or diene is increased. Tables 1 and 2 summarize results of intramolecular Diels-Alder reactions that provide a test of this propo-sai.24.25 pirst, it is clear that an electron-releasing Et2N group at C(9) of the nonatrienoate system leads to a substantial increase in selectivity for the tranj-fused product (compare entries 4-6, Table 1). Increased trans stereoselectivity also occurs with C(9)-alkoxy-substituted nonatrienes. A similar effect... 

Yamamoto has also shown that the hydrogen is selectively removed from the trans alkyl group. " Ene reaction of (91) catalyzed by (93) gives (95) in 89% yield in 91% enantiomeric excess. Similar cycliza-tion of (92) gives (96) in 83% yield in 32% enantiomeric excess. The ene reactions of (85), (90), (91) and (92) indicate that tranj-l-alkenylcyclohexanols are produced selectively in type I reactions (Scheme 16). 

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