1- Octenyl iodide

Retention of the stereo- and regiochemical identity of y monosubstituted allylic electrophiles is generally more difficult than that of -y,y-disubstituted analogs. Nonetheless, the Pd-catalyzed reaction of lithium cyclopentenolate in the presence of 2 equiv of BEts with ( )- or (Z)-2-octenyl acetate (but not chloride or bromide) proceeds satisfactorily, producing only minor amounts of undesirable by-prodncts (Table 2). High stereospecificity figures are, in fact, observable in the uncatalyzed reaction of lithium cyclopentenolate with (Z)-2-octenyl iodide and bromide, but the product yields were substantially lower. So, those results that are satisfactory in an overall sense are obtainable only in cases where the reaction is run with 2-octenyl acetate in the presence of BEts and a Pd catalyst. 

The present preparation illustrates a general and convenient method for the fnms-iodopropenylation of an alkyl halide.4 The iodopropenyl-ated material is not usually stable but is a useful synthetic intermediate. For example, it forms a stable crystalline triphenylphosphonium salt for use in the Wittig reaction, and under Kornblum reaction conditions (DMS0-NaHC03, 130°, 3 minutes) it gives an (E)-a,/9-unsaturated aldehyde.4 In addition to the phosphonium salt described in Note 15, the following have been prepared (4-p-methoxyphenyl-2-butenyl)-triphenylphosphonium iodide [Phosphonium, [4-(4-methoxyphenyl)-2-butenyl]triphenyl-, iodide], m.p. 123-127° (2-octenyl)triphenyl-phosphonium iodide [Phosphonium, 2-octenyltriphenyl-, iodide], m.p. 98° and (2-octadecenyl)triphenylphosphonium iodide [Phosphonium, 2-octadecenyltriphenyl-, iodide], m.p. 50°. 

The turnover numbers for reactions of ( )-l-octenyl metals with phenyl iodide in the presence of Pd(PPh3>4 in THF at room temperature were 2 (Al), 3 (Zr) and 2000 (Zn). See ref. 239a. 

A soln. of methyl l-(l,3-dithian-2-ylmethyl)-c/5-l-methylcyclohex-2-ylacetate and methyl iodide stirred 12 hrs. at room temp., excess methyl iodide removed in vacuo, the soln. of the intermediate crude sulfonium salt in tetrahydrofuran added to NaH in tetrahydrofuran, and stirred 2.5 hrs. methyl l-(3,7-dithia-rran5--l-octenyl)-cw-l-methylcyclohex-2-ylacetate. Y 86%. F. method s. J. A. Marshall and D. E. Seitz, J. Org. Chem. 40, 534 (1975). 

Geospecific replacement. 1-Octyne and catecholborane stirred 2 hrs. at 70° under Ng, cooled to room temp., and stirred 2 hrs. at 25° with water -> frans-l-octenyl-boronic acid (Y 90%) dissolved in ether, cooled to 0°, aq. 3 N NaOH added followed at 0° by 20% excess iodine in ether with stirring, which is continued 0.5 hr. at 0° -> trans-l-ocitnyX iodide (Y 80%). Overall Y 71%. F. e. s. H. C. Brown, T. Hamaoka, and N. Ravindran, Am. Soc. 95, 5786 (1973) also cis-a,p-ethylenebromides with inversion of configuration s. ibid. 95, 6456 cis- and trans- ,/ -ethylenehalides via enesilanes cf. R. B. Miller and T. Reidienbadi, Tetrah. Let. 1974, 543. 

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