Intramolecular addition modes

Intramolecular Addition Modes in Radical Cyclopolymerization of Some Unconjugated Dienes... 

The factors influencing intramolecular addition modes were investigated in detail in the radical cyclopolymerization of some unconjugated dienes. 

Thus, we investigated in detail the factors influencing intramolecular addition modes in the radical cyclopolymerization of some unconjugated dienes, including diallyl and dimethallyl dicarboxy-lates, acrylic and methacrylic anhydrides, and allyl -substituted acrylates and discussed the selectivity of reaction mode of intramolecular hh or ht addition in terms of the thermodynamical standpoint. The present article gives a summary of our recent work including published papers(18-23). 

On the other hand, we reexamined in detail the ring size of the cyclic structural units of poly-AA s by means of IR, 1H-NMR, and C-NMR spectroscopy these analytical procedures were applied to the structural analysis of poly-AA, the poly(acrylic acid) derived from hydrolysis of the poly-AA, and the poly(methyl acrylate) obtained by subsequent esterification of the poly(acryl-ic acid) in comparison with the corresponding model polymers of five- or six-membered ring structure. Then, we investigated in detail the effects of polymerization conditions on the ring size of poly-AA s, i.e., on the intramolecular addition modes in the cyclopolymerization of AA since five- or six-membered ring anhydride structure can be formed via intramolecular hh or ht addition of the uncyclized radical to the internal double bond(22,23). 

In addition to nucleophilic reactions, Baldwin s rules also apply to homo-lytic and cationic processes. Table 21 lists rate constants for ring closure of lower -alkenyl radicals (71), in which intramolecular addition to the double bond occurs in the exo-mode (Beckwith, 1981). It is unfortunate that EM-... 

The Fe111/11 case is particularly simple. For electron transfer reactions in general, several normal modes may contribute to the trapping of the exchanging electron at a particular site. In addition, intramolecular vibrational modes are of relatively high frequency, 200-4000 cm-1, and at room temperature the classical approximation is not valid since only the v = 0 level is appreciably populated. In order to treat the problem more generally, it is necessary to turn to the quantum mechanical results in a later section. 

The ethoxycarbocation intermediate (363) produced by the action of acid on the cyclobutenedione monoacetal (362) has been found to react with bis(trimethylsilyl)-acetylene to afford a 2-methylenecyclopent-4-ene-l,3-dione derivative (365). The authors426 proposed that the rearrangement results from an unprecedented cationic 1,2-silyl migration on the alkynylsilane, subsequent ring expansion via a vinyl cation intermediate (364), and re-closure by intramolecular addition of an acyl cation to a silylallene in a 5-exo-trig mode (see Scheme 90). 

The inelastic neutron TOF spectrum of a butane monolayer adsorbed on Carbopack B at 80 K (10) is shown at the top of Fig. 6. The background inelastic scattering from the substrate has been subtracted. Typical counting time for such a spectrum is -100 hours. The intramolecular torsional modes of the CH, and CH groups observed in the bulk liquid and solid (23) are also found in the monolayer spectrum. In the two methyl torsionsal modes the CH, groups rotate either in the same or opposite sense about the terminal C-C bonds, and in the CH2-CH torsion the two halves of the molecule rotate in the opposite sense about the internal C-C bond. In addition to the intramolecular torsional modes, new features appear in the monolayer spectrum which are not observed in bulk samples an intense peak at -112 cm"-1 and a broader band centered at 50 cm-1. 

Competition between the j8,y- and the a,/ -elimination-addition modes is possible in the systems studied by Bottini and coworkers. N-(2-Bromoallyl)alkylamine (199) with NaNH2 in liquid NH3 gives mainly l-alkyl-2-methyleneaziridine (200) together with a lower amount of N-alkylpropargylamine (201) (Pollard and Parcell, 1951 Bottini and Roberts, 1957). The driving force for this intramolecular substitution of the unactivated vinyl bromide (199) is probably the presence of the... 

Metal-mediated intramolecular addition of silyl enolates to alkynes is also valuable for the synthesis of cyclic ketones. A stoichiometric amount of HgCl2 or EtAlCl2 effectively promotes the cycloalkenylation via anti-addition to alkynes (Equations (87) and (88)).319 320a The -addition mode can be explained by a metal coordination to the triple bond and subsequent attack of the enolate moiety from the opposite side to the metal. The resultant alkenylmetals can be used for carbon-carbon and carbon-heteroatom bond formation as well as protonation. 

Enchaining radical cyclizations steps to provide polycyclic compounds is the simplest approach. Because the 5-exo cychzation is the most straightforward mode of cychzation, polyquinanes have been the object of many studies [20]. Roimd-trip strategies as defined by Haney and Curran [21], from a vinyl radical such as 8 have been developed by Takasu et al. [22] and revisited by Tripp et al. (Scheme 3) [23]. Mixtures of diastereomers 9 are obtained from hnear precursor 7. The same group has examined the intramolecular addition of a vinyl radical onto a dienoate to produce [4 -l-1]- or [4 + 2]-annulated compounds [24]. Tandem 5-exo-trig cyclizations have also been shown to yield tricyclo[6.2.1.0 ]undecan-4-one and related polycyclic compounds, using a nickel-catalyzed electroreduction [25]. 

Grande s group has studied the titanocene-promoted intramolecular addition of epoxides to activated alkenes in both 5-exo and 6-endo cyclization modes as a new way of preparing polycyclic b-lactam antibiotics [ 110-112]. 

Free-radical cyclization reactions (i.e., the intramolecular addition of an alkyl radical to a C=C ir bond) have emerged as one of the most interesting and widespread applications of free-radical chemistry to organic synthesis. Free-radical cyclizations are useful because they are so fast. The cyclization of the 5-hexenyl radical to the cyclopentylmethyl radical is very fast, occurring at a rate of about 1.0 X 105 s-1. In fact, the rate of formation of the cyclopentylmethyl radical is much faster than the rate of cyclization to the lower energy cyclohexyl radical. This stereoelectronic effect is derived from the fact that the overlap between the p orbital of the radical and the rr MO of the double bond is much better when Cl attacks C5 than when it attacks C6. The relative rates of 5-exo and 6-endo ring closures are strongly dependent on the nature of the substrate and especially on the amount of substitution on the ir bond. Cyclization of the 6-heptenyl radical in the 6-exo mode is also very favorable. 

The unsaturated 6-lactone (84) undergoes intramolecular photochemical (2 + 2)-cycloaddition to give (85)." The scope of the process has been evaluated and the 5-lactones (86-88) all behave similarly, affording the products shown in Scheme 2. The lactones (86) and (87) both cyclise in the two possible modes. Intramolecular cycloaddition reactions within polymethyldia-minebis(4-methyl-7-coumarinyl)oxyacetamides have been described. Zhu and Wu have reported that a biscoumarin system linked by a phenanthroline unit does not undergo photodimerisation. Instead, intramolecular addition of a coumarin unit to the phenanthroline occurs. 

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