Pentadienyl vinyl

Hydrosilylation of I-vinyl-1-cyclohexene (77) proceeds stereoselectively to give the (Z)-l-ethylidene-2-silylcyclohexane 78, which is converted into (Z)-2-ethylidenecyclohe.xanol (79)[74]. Hydrosilylation of cyclopentadiene affords the 3-silylated 1-cyclopentene 80. which is an allylic silane and used for further transformations[75.75a]. Cyclization of the 1,3,8, lO-undecatetraene system in the di(2.4-pentadienyl)malonate 69 via hydrosilylation gives the cyclopentane derivative 81. which corresponds to 2.6-octadienylsilanc[l8,76]. 

New photochromic dyes with electrocycHc reactions have been proposed on the basis of 1,5-electtocycHzation of heterogenous pentadienyl—anions (124). StiH newer are investigations into the photocycHzation of 2,4,6-tri-isoptopylbenzophenones for vinyl polymers ia the glassy state (133). 

Allylic radical are relatively stable, and the pentadienyl radical is particularly stable. In such molecules, (E), E), (E),(Z), and (Z),(Z) stereoisomers can form. It has been calculated that (Z),(Z)-pentadienyl radical is 5.6 kcal mol less stable than the ( ),( )-pentadienyl radical. ° It is noted that vinyl radical have (E) and (Z) forms and the inversion barrier from one to the other increases as the electronegativity of substituents increase. Enolate radicals are also known. ... 

Participation by cumulative double bonds and vinyl cation intermediates has been suggested in the solvolyses of a number of homoallenyl systems. Hanack and Haffner (87) reported the solvolyses of 3,4-pentadienyl jS-naphthalene sulfonate, 110 (R = H) under a variety of conditions. The products... 

The regioselectivity in palladium-catalyzed alkylations has been attributed to the dynamic behavior of trihapto pentadienyl metal complexes60. For example, competing electronic and steric effects influence product formation in dienyl epoxides, but in palladium-catalyzed reactions steric factors were often found to be more important. Thus, alkylation of dienyl epoxide 76 with bulky nucleophiles such as bis(benzenesulfonyl)me-thane in the presence of (Ph3P)4Pd occurred exclusively at the terminal carbon of the dienyl system producing allyl alcohol 77 (equation 39). However, the steric factors could be overcome by electronic effects when one of the terminal vinylic protons was replaced with an electron-withdrawing group. Thus, alkylation of dienyl epoxide 78 affords homoal-lylic alcohol 79 as the major product (equation 40). 

Short branches, specifically ethyl branches up to about 2 mol%, are formed in the polymerization of ethylene by meso-ansa zirconocenes containing unsubstituted cyclo-pentadienyl and indenyl ligands [Melillo et al., 2002]. Ethyl branches form by an isomerization process in which the usual P-hydride transfer to monomer is immediately followed by reinsertion of the vinyl-terminated polymer into the formed ethyl-zirconium bond. 

Figure 11.5. SHMO frontier orbitals and total energies for vinyl-substituted pentadienyl cations.

Pentadienoic acid reacts well with aromatic halides to give 5-aryl-pentadienoic acids. The only vinylic halide studied so far is E-2-bromostyrene. This halide gave a 57% yield of E,E,E-7-phenylheptatrienoic acid.N-(2,4-Pentadienyl)piperidine is very useful... 

The C-H bond dissociation energies (BDEs) decrease in the sequence vinylic phenylic > primary > secondary > tertiary > allylic > pentadienylic = benzylic considerably (Table 6.3). 

Efficient methods for the preparation of pentadienyl compounds of the alkali metals have now been developed. Treatment of 1,4-dienes with butyllithium in the presence of tetrahydrofuran (thf) at —78° yields deep orange solutions which contain pentadienyllithiums (36,37). Any excess butyllithium may be destroyed by its reaction with thf by allowing the mixture to warm up briefly to room temperature (38). Similar results are obtained using potassium amide in liquid ammonia (39). 1,3-Dienes, however, do not yield pentadienyl anions under these conditions, unless the diene is conjugated with a phenyl (40), vinyl (41), trimethylsilyl (48), or similar stabilizing group. Unfortunately, 1,4-dienes are not very readily accessible. However, 1,3- as well as 1,4-dienes can be metallated using a 1 1 mixture of butyllithium and potassium tm-butoxide (49). Trimethylsilylmethylpotassium is also effective (44). 

The molecular structures of three >/3-pentadienyl complexes having W, S, and U configurations, respectively, are shown in Fig. 5. Apart from showing the short uncoordinated C=C bond of the vinyl system a common feature is the unsymmetrical bonding of the fj3-allyl group with the longest M—C bond to the atom which bears the vinyl substituent (149). 

Pentadienyl-terminated poly(methyl methacrylate) (PMMA) as well as PSt, 12, have been prepared by radical polymerization via addition-fragmentation chain transfer mechanism, and radically copolymerized with St and MMA, respectively, to give PSt-g-PMMA and PMMA-g-PSt [17, 18]. Metal-free anionic polymerization of tert-butyl acrylate (TBA) initiated with a carbanion from diethyl 2-vinyloxyethylmalonate produced vinyl ether-functionalized PTBA macromonomer, 13 [19]. 

Bis- [4-chlor-phenyl]-methyl-phosphanoxid221 Bis-[4-trimethylsilyl-phenyl]-phenyl-phosphanoxid222 Diethyl-(2-phenyl-vinyl)-phosphanoxid222 Diethyl-1,3-pentadienyl-phosphanoxid22 ... 

Complexes (160) (see equation 35) undergo conversion to phenols upon thermolysis. Alternatively, treatment with AICI3 under a CO atmosphere gives an j)" -iron cyclohexadienone complex thermolysis or treatment with CuCl2 affords a phenol as well. Complexes (162), derived from nucleophihc addition to ( ) -pentadienyl)Fe(CO)3+ cations (see equation 37), can be converted to vinyl cyclopropanes by using CAN (equation 41). ... 

A (7] -allyl)ferralactam synthesis using Ee2(CO>9 has been reported by Aumann el a/. <1979CB3644>. Schobert el a/. have also studied the regioselective reactions of (4,6- 7 -pentadienyl)ferralactones 53 with primary amines to afford 3-( o-vinyl)-(4,6-7] -allyl)ferralactams 54 and 6-(-vinyl)-(4,6- -allyl)ferralactams 55 (Equation 7) <2004JOM575>. 

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