F Cyclopentene

Cyclopentadienylsodium, 1849 p-Cyclopentadienyltrimethyltitanium, 3033 f Cyclopentane, 1933 Cyclopentanone, 1899 Cyclopentanone oxime, 1926 f Cyclopentene, 1885 f Cyclopentylamine, 1985... 

AhydH °f cyclopentene to produce cyclopentane is smaller than it is in cyclohexene because of crowding of hydrogen atoms in the smaller product molecule relative to the larger one. 

Low-valent rhenium complexes with Tp and bpy (bpy = bipyridine) ligands that do not include CO in the coordination sphere have been synthesized. Complexes of the type TpRe(bpy)Y (Y = Cl or cyclopentene bpy = 2,2 -bipyridyl) are derived from [TpRe bpy)Cl][OTf with the accompanying one or two electron reduction by Zn/Hg or Na/Hg amalgam, respectively (Scheme 60). " TpRe(bpy)(f/ -cyclopentene) is a potent 7i-base as evidenced by the II/I oxidation potential of —0.66 V versus NHE, 0.89 V more cathodic than TpRe(CO)(PMe3)( -cyclohexene). 

The photochemical [2 + 2] cycloaddition of cyclopentene to pentaflu-oropyridine in cyclohexane gave a 1 1 adduct, which in excess olefin gave a single 1 2 adduct (37) (82JOC4462). The solvent has an important role, as in its absence two 1 2 adducts are obtained. With PhC CR in cyclohexane, the nature of R determined whether a triene (R = f-butyl) or tetraene (R = Me) was in the product mixture (89T1755). A mixture of 1 2 and two 1 1 adducts was obtained by [2 + 2] addition of but-2-yne in the absence of a solvent [87JFC(20)745]. 

Wahrend Heptafluor-l-methylamino-3-methylimino-cyclohexen sich ohne Schwierig-keit unter C-F-Hydrogenolyse zum entsprechenden Benzol-Derivat reduzieren laBt (s. S. 615), wird beim entsprechenden Cyclopenten-Derivat lediglich die C=N-Doppelbindung hydriert1 ... 

It was envisioned that hydrindanone 83 and cyclopentene 85 could be used as intermediates in the synthesis of e f-retigeranic acid A (1) and e f-retigeranic acid B (2), respectively. To prepare the building block 90, cyclopentene 85 was reduced with diimide (93 %) in order to prevent isomerization and subsequently deprotected with PPTS to yield hydrindanone 90 (quant.), which could provide access to <77/-retigeranic acid B (2) (Scheme 10.7). Hydrindanone 83 was reduced via an enol triflate and then subjected to Pd-catalyzed reduction to provide cyclopentene 91 (87 % from 83). Upon hydrogenation of 91 with Pd/C and cleavage of the acetal with iodine, protected hydrindanone 92 (95 % from 91) was obtained. The deprotection of 92 provided ent-60, whose enantiomer was used in previous syntheses of retigeranic acid A (1) by Corey [14] and Hudlicky [46, 47]. 

The first phase of our efforts was the unambiguous synthesis of each model substrate. PN and PX were already well characterized materials (1) While direct synthesis of the phenyl and carbomethoxy compounds from PN and/or PX was attempted, this approach was unsuccessful due to the sluggish reactivity of the norbornenyl double bonds in these molecules (2). A successful approach to CBN and (fiBN based on N-phenyl maleimide (NPMI) trapping of the respective thermodynamically favored 1-substituted cyclopentadienes is shown in Equation 1. Similarly, kinetic trapping of 2-phenyl cyclopentadiene, from the in situ dehydration of 3-hydroxy, 3-phenyl cyclopentene, gives a clean yield of (f)VN (Equation 2). The remaining phenyl isomer (VX) and the three other carbomethoxy isomers (CBX, CVN, CVX) were all obtained by the thermal isomerization chemistry described in the next section of this paper. They were each isolated in pure form by liquid chromatography We were unable to obtain any (f)BX or any of the 7-substituted isomers by any means. 

Campos et al. reported asymmetric synthesis of the DP receptor antagonist 42 starting from (f )-2-cyclopentene-1-acetic acid obtained via asymmetric allylic... 

Although the catalytic reactions described above involve mononuclear Rh and Rh complexes, dinuclear Rh compoimds have also been studied as catalyst precursors in oxygenation reactions. The system [Rh2(p.-OAc)4]/ f-BuOOH is effective in the oxidation of cyclic alkenes such as cyclopentene, cyclohexene and cycloheptene, mainly to o, /i-unsaturated ketones and allylic acetates, but with poor yields (Eq. 4) [30,31]. 

A plausible mechanism involves the reaction of the dihydride precursor with t-butylethylene to the 14-e complex [Ir(C6H3-2,6 CH2P-f-Bu2 2)]> which undergoes the oxidative-addition reaction of the alcohol to afford a hydride alkoxide complex. Further /i-hydride ehmination gives the alde-hyde/ketone and regenerates the dihydride active species [55]. In the particular case of 2,5-hexanediol as the substrate, the product is the cycHc ketone 3-methyl-2-cyclopenten-l-one. The formation of this ketone involves the oxidation of both OH groups to 2,5-hexanedione followed by an internal aldol reaction and further oxidation as in the final step of a Robinson annotation reaction [56]. 

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