6-heptenyl

Interesdng intramolecular cycllzadon of Tnitroalkyl radicals generated by one-electron oxidadon of nci-nitro anions vrith CAN is reported. As shown in Eq. 5.44, stereoselecdve formadon of 3,4-funcdonalized tetrahydroflrtans is observed. TNitro-6-heptenyl radicals generated by one electron oxidadon of aci-nitroanions vrith CAN afford 2,3,4-trisnbsdtuted tetrahydropyrans. The requisite nitro compounds are prepared by the Michael addidon of 3-buten-Tal to nitroalkenes. 

It was proposed that the transition state requires approach of the radical directly above the site of attack and perpendicular to the plane containing the carbon-carbon double bond. An examination of molecular models shows that for the 3-butenyl and 4-pentenyl radicals (16, =1,2) such a transition state can only be reasonably achieved in < Xf>-cyclization (i.e. 16—> 15). With the 5-hexcnyl and 6-heptenyl radicals (16, w=3,4), the transition state for exo-cyclization (16- 15) is more easily achieved than that for enc/o-cyclization (i.e. 16 — 17). 

HEMA see hydroxycthyl methacrylate 6-heptenyl radicals, cyeli/ation 23, 193... 

Fig. 10.13. MM2 models of exo and endo cyclization transition structures for 5-hexenyl, 6-heptenyl, and 7-octenyl radicals. Reproduced from Tetrahedron, 41, 3925 (1985), by permission of Elsevier.

One of the few examples of a synthetically useful 6-exo-trig cyclization from 3-aza-6-heptenyl radicals is found in the total synthesis of ( )-melinonine-E (159, Scheme 31) by Bonjoch et al. [66]. The cyclization precursor, a,P-unsaturated nitrile 157 was prepared from 1,4-cyclohexanedione monoethylene acetal (156) and tryptamine in 5 steps with 41% overall yield. Initially, when 157 was treated with 1.1 equiv. of n-BujSnH and 0.1 equiv. of AIBN in toluene for 16 h, the expected cyclization to the 2-azabicyclo[3.3.1]nonane ring took place to give 158 only as a minor product, along with its C(14) chloro- and dichloro-substituted derivatives as major products. An additional treatment of the crude mixture with 2.2 equiv. of BujSnH brought about the reduction of the C-Cl bonds to provide nitrile 158 in 38% yield over... 

Scheme 31. A 6-exo-trig cyclization from a 3-aza-6-heptenyl radical in the total synthesis of ( )-melinonine-E...

Dimethyl-5-(3,7-dimethyl- -6-heptenyl)pyrazine R3 ch3 CH(CH3) = ch3 =CHCH2 CH2CH(CH3)CH2CH2-... 

Cobalt catalysed allylation of a primary dialkylzinc preparation of 6-heptenyl pivalate25... 

Heptenyl-type radicals preferentially undergo 6-exo instead of 1-endo cyclizations <85T3925 01OL2217>. 6-Exo cyclizations nevertheless are generally slower than the related... 

Enholm s strategy [26] involves incorporation of all the structural features required for the 6-heptenyl radical cychzation reaction into the monomer subunit prior to metathesis polymerization, thus ensuring maximum possible loading. Although several steps are needed to prepare the monomer unit and recycling the support is not possible, this work does show the potential of using chiral linking imits to control the stereochemistry of radical cycliza-tions on polymer supports. 

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. 

Ethyl 3,3-Dicydopropyl- 2312 (5-Mcthylen-6-heptenyl) 2280 (5,7-Octadienyl)- 2280 Bicyclo 5.3.0 dec-l-ene... 

In the case of a 2-isopropenyl-substituted 5-hexenyl radical, derived from 2-(2-oxo-6-heptenyl)-l,3-o.xathiolan-5-one, the major product arises from a chairlike conformation of the transition state with both substituents in an equatorial position13,14. Base hydrolysis gives 2-isopropenyl-5-methylcyclopentanol (transicis 8 1) in 90% yield. 

Scheme 2.32. The effect of pressure on the cyclization of 5-hexenyl and 6-heptenyl, respectively. Transition structures of the endo-trig and exo-trig cyclization.

Hydroxy [158697-56-4]. 4-(3-Hydroxy-7-phenyl-6-heptenyl)- ,2-benzenediol, 9CI. l-(3,4-Dihydroxypheny[)-7-phenyl-6-hepten-3-ol C19H22O3 M 298.381 Constit. of the rhizomes of C. xanthorrhiza (Zingiberaceae). Cryst. (CHCI3/C6H6). Mp 100-102°. 

Heptenyl glucosinolate, H-8 5-Hexenyl glucosinolate, H-82 Hexyl glucosinolate, H-118... 

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