Disubstituted norbornenes

TABLE 9. ROMP of 5,6-disubstituted norbornenes (both substituents the same)... 

A double mesogen density is easily achieved by using disubstituted norbornene monomers of type IV-n and V-n (Fig. 4). 

Ungerank et al. investigated the influence of different molybdenum Schrock-type initiators 1, 2 and 3 (see Fig. 2) on the polymerization of ( )- and (-)-exo,e tdo-bis[4 -cyanobiphenyl-4-yl)oxyalkyl]norborn-5-ene-2,3-dicarboxy-lates [( )-IV-n and (-)-IV-n] [47]. The initiator had a strong influence on the Z/E ratio of the double bond in the polymer chain and therefore also on the tacticity of the polymer chain. Using racemic 2,3-disubstituted norbornene derivatives, such as ( )-IV-n, the two adjacent monomers (diads) can in principle form eight different stereoisomers, as depicted in Fig. 5 [48]. 

Williams, L. Paddon-Row, M. N. Electrostatic and steric control of Jt-facial stereoselectivity in nucleophilic additions of LiH and McLi to endo-5,6-disubstituted norbornen-7-ones an ab initio MO study, J. Chem. Soc. Chem. Commun. 1994, 353-355. 

Disubstituted norbornene derivatives 14 give 2,3-e3to-eis-oxiranes with MCPBA. With the cyclopentane ring fixed in the envelope form, there is total stereoselectivity (Eq. 5). ... 

It should be noted that in the case of the disubstituted norbornene macromonomer... 

O DeU, R. McConviUe, D. H. Hofmeister, G. E. Schrock, R. R. Polymerization of enantiomeric-aUy pure 2,3-dicarboalkoxynorbornadienes and 5,6-disubstituted norbornenes by well-characterized molybdenum ring-opening metathesis polymerization initiators. Direct determination of tacticity in cis, highly tactic and trans, highly tactic polymers. /. Am. Chem. Soc. 1994, 116, 3414-3423. 

Figure 11 Four possible regular microstructures of polymer made from 5,6-disubstituted norbornene by ROMP.

Similarly to aromatic n system, olefinic --electron donors also readily react with bissulfonyl peroxides. Norbornene, when reacted with bis(arylsulfonyl) peroxides, gives a disubstituted product following Wagner-Meerwein rearrangement (equation 6)42. 

Metal-norbornene complexes are much more stable than the corresponding complexes with other disubstituted alkenes. This is due to the... 

A highly regio- and enantio-selective hydroformylation of alkenes, such as PhCH= CH2, CH2=CHCH2CN, and CH2=CHOAc, catalysed by ruthenium complexes with (g) 2,5-disubstituted phospholane ligands has been reported. With (83) as the ligand, the turnover rates over 4000 h-1 at 80 °C, have been attained.108 (Acac)Rh(CO)2-TangPhos [Tangphos = (84)] has been developed as a new enantioselective catalyst for asymmetric hydroformylation of norbornene and other [2.2.1]-bicyclic alkenes (55-92% ee).109... 

Boamfa et al. investigated macroscopic orientation of disubstituted cyano-biphenyl poly(norbornene) IV-n (n=3,5) using different magnetic fields of up to 20 T. Both the degree of orientation and optical properties were compared with a cyanobiphenyl-substituted acrylate polymer with a spacer of four methylene units [49,50]. 

The diastereomeric ratio is high only for ( )-disubstituted alkenes and norbornene, but low for cyclic and (Z)-alkenes, reflecting the order of stability of the intermediate complexes. The loss of stereochemical purity is probably due to base-catalyzed nitroso-oxime tautomerization during the reduction. However, the use of diisobutylaluminum hydride, before adding lithium aluminum hydride, allows (3/ , 4S )-3,4-hexanediamine to be obtained from (Z)-3-hexene with d.r. [(3R, 4S )IQR AR )] 90 10. 

The cycloaddition of 3. M,2,4-triazole-3,5(4f/)-diones to the norbornene-fused cyclopentadi-enes (dehydroisocyclopentadienes or tricyclo[5.2.1.02-6]deca-2,5,8-trienes) usually proceeds from below the plane of the cyclopentadiene to give the adducts 36 with the synsesquinctrbor-nene structure, but loss of stereocontrol is observed due to geminal disubstitution at C-4. 

Oxymercaration (2, 265-267 3. 194). Brown and Geoghegan have investigated the relative reactivities of a number of olefins in the oxymercuration reaction in a 20 80 (v/v) mixture of water and THF. The following reactivity is observed terminal disubstituted > terminal monosubstituted > internal disubstituted > internal trisub-stituted > internal leirasubstitu ted. Thus steric factors play a major role in the reactivity of olefins. Increased substitution on the double bond and increased steric hindrance at the site of hydroxyl or mercury substituent attachment decrease the rate of reaction. In the case of olefins of the type RCH CHR, cts-oleiins are more reactive than the corre.sponding rra/i.s-olefins. Inclusion of the double bond in ring systems causes a moderate rate increase which varies somewhat with structure cyclohcxenc > cyclo-pentenc cyclooctene norbornene bicyclo[2.2.2]-octene-2. 

Contrary to the parent compound, double bond disubstituted methylenecyclopropanes (70) react with Ni(0) or Pd(0) catalysts by cleavage of the C(2)-C(3) bond. In the presence of olefins such as ethylene, styrene or norbornene a relatively mild cyclodimerization into methylenecyclopentanes (71-73) is achieved in 75% or better yields (equation 47) . 

The reaction of 1,1-disubstituted olefins 29 [14, 23, 24, 27] usually requires higher reaction temperature than that of styrene or norbornene, and the enan-... 

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