This contradictory response was started last night, before it became contradictory.
There are numerous literature references for the SN
2 substitution of the OH in cinnamyl alcohol for chloride, bromide and iodide, using HCl, HBr and HI respectively. In fact, HI can go on to reduce the alkyl iodide to give the ever-usable propenylbenzene in one-pot.
The substitution works probably because of the conjugation of the molecule, which gives a greatly stabilised transition state for the SN
2 displacement (much like the rate enhancing effects when a leaving group is
alpha- to a ketone). The addition across the double bond happens at its usual (slower) rate; addition across the double bond also disrupts the favourable conjugation. Because of these effects, the -OH of cinnamyl alcohol behaves effectively like the reactive -OH of benzyl alcohol.
I would suggest adding HBr to cinnamyl alcohol to give cinnamyl bromide, followed by reduction to propenylbenzene with borohydride/PTC. Many reductions give a mixture of products (e.g. allylbenzene/propenylbenzene/propylbenzene) but with a suitable hydride nucleophile you can selectively displace the bromide with hydride (again, this may be made easier because of the conjugation stabilising the transition state).
Here are some references (some of which are available online for free). Some of them look very interesting:
Cinnamyl chloride from cinnamyl alcohol with HClJ.Amer.Chem.Soc. 107 (7), 1985, 2033-2046
Chem.Ber.,
39, 1906, 2553
Arch.Pharm.(Weinheim Ger.), 247, 1909, 349
J.Org.Chem.,
42, 1977, 871-875
Justus Liebigs Ann. Chem.,
479, 1930, 211, 248
J.Chem.Soc., 1941, 507, 510.
Cinnamyl chloride from cinnamyl alcohol using other sources of chlorideSOCl2, 94% yield: Org.Lett.,
5 (
, 2003, 1167-1170
PPh3/trichlorocyanuric acid: Synth.Commun.,
32 (17) 2002, 2691-2694
Trichlorocyanuric acid/DMF/DCM, 92% yield: Org.Lett. 4 (4), 2002, 553-556
SOCl2/benzotriazole, 100% yield: Syn.Lett.,
11, 1999, 1763-1765
Potassium carbonate/chlorotrimethylsilane, 91% yield: Synthesis,
4, 1983, 314-315 [Article in German].
Cinnamyl bromide from cinnamyl alcohol with HBrJ.Amer.Chem.Soc. 38, 1916, 1076
Chem.Ber.,
58, 1925, 280
J.Org.Chem.,
25, 1960, 1719-1722
J.Chem.Soc.,
97, 1910, 426
Chem.Ber. 39, 1906, 2553.
Cinnamyl bromide from cinnamyl alcohol using other sources of bromide
PBr3: Chem.Ber. 43, 1910, 178
NaBr/BF3/acetonitrile (79% yield): Tetrahedron Lett.,
26 (32), 1985, 3863-3866
Hexamethyldisilane/pyridinium bromide perbromide (100% yield): J.Org.Chem. 45 (9), 1980, 1638-1639
Chlorotrimethylsilane/lithium bromide (93% yield): J.Org.Chem.,
45 (9), 1980, 1638-1639.
Cinnamyl iodide from cinnamyl alcohol with HIJustus Liebigs Ann. Chem. 479, 1930, 211, 248.
Cinnamyl alcohol to propenylbenzene with HIChem.Ber.,
11, 1878, 671.
Reduction of cinnamyl bromide to propenylbenzene
NaBH4/PTC, 80% yield: J.Org.Chem.,
46 (19), 1981, 3909-3911
Lithium tri-sec butyl borohydride, 99% yield: Bull.Chem.Soc.Jpn.,
58 (2), 1985, 789-790
Zn(BH4)2, 60% yield: Angew.Chem.,
95 (7), 1983, 568-569 [Article in German]
LiAlH(i-Bu)2(n-Bu), 95% yield: J.Org.Chem. 49 (10), 1984, 1717-1724.
