A Photoirradiative Phase-Vanishing Method: Efficient Generation of HBr from Alkanes and Molecular Bromine and Its Use for Subsequent Radical Addition to Terminal Alkenes

Abstract

A triphasic phase-vanishing (PV) system comprised of an alkane, perfluorohexanes, and bromine was successfully combined by photoirradiation to efficiently generate hydrogen bromide, which underwent radical addition with 1-alkenes in the hydrocarbon layer to afford terminal bromides in high yields.

Key words

fluorous solvent - phase-vanishing - photoirradiation - bromination - hydrogen bromide

References and Notes

• 1 For a general review on fluorous chemistry, see: Handbook of Fluorous Chemistry   Gladysz JA. Curran DP. Horváth IT. Wiley-VCH; Weinheim: 2004. 
• For reviews on fluorous solvents, see:
• 2a Ryu I. Matsubara H. Emnet C. Gladysz JA. Takeuchi S. Nakamura Y. Curran DP. In Green Reaction Media in Organic Synthesis   Mikami K. Blackwell Publishing; Oxford: 2005.  p.59 
• 2b Matsubara H. Ryu I. In Green Separation Processes: Fundamentals and Applications   Afonso CAM. Crespo JG. Wiley-VCH; Weinheim: 2005.  p.219 
• 3 Matsubara H. Yasuda S. Sugiyama H. Ryu I. Fujii Y. Kita K. Tetrahedron  2002,  58:  4071 
• 4 Matsubara H. Maeda L. Ryu I. Chem. Lett.  2005,  34:  1548 
• 5 Matsubara H. Maeda L. Sugiyama H. Ryu I. Synthesis  2007,  2901 
• For reviews on the ‘Phase-Vanishing’ method, see:
• 6a Ryu I. Matsubara H. Nakamura H. Curran DP. Chem. Rec.  2008,  8:  351 
• 6b Iskra J. Lett. Org. Chem.  2006,  3:  170 
• 7 Ryu I. Matsubara H. Yasuda S. Nakamura H. Curran DP. J. Am. Chem. Soc.  2002,  124:  12946 
• 8a Nakamura H. Usui T. Kuroda H. Ryu I. Matsubara H. Yasuda S. Curran DP. Org. Lett.  2003,  5:  1167 
• 8b Matsubara H. Yasuda S. Ryu I. Synlett  2003,  247 
• 8c Rahman MT. Kamata N. Matsubara H. Ryu I. Synlett  2005,  2664 
• 8d Matsubara H. Tsukida M. Yasuda S. Ryu I. J. Fluorine Chem.  2008,  129:  951 
• 9a Jana NK. Verkade JG. Org. Lett.  2003,  5:  3787 
• 9b Iskra J. Stavber S. Zupan M. Chem. Commun.  2003,  2496 
• 9c Curran DP. Werner S. Org. Lett.  2004,  6:  1021 
• 9d Podgoršek A. Stavber S. Zupan M. Iskra J. Eur. J. Org. Chem.  2006,  483 
• 9e Windmon N. Dragojlovic V. Tetrahedron Lett.  2008,  49:  6543 
• 9f Windmon N. Dragojlovic V. Beilstein J. Org. Chem.  2008,  4:  29 
• 9g Ma K. Li S. Weiss RG. Org. Lett.  2008,  10:  4155 
• 9h van Zee NJ. Dragojlovic V. Org. Lett.  2009,  11:  3190 
• 9i Pels K. Dragojlovic V. Beilstein J. Org. Chem.  2009,  5:  75 
• 11a Brown HC. Lane CF. J. Am. Chem. Soc.  1970,  92:  7212 
• 11b Brown HC. Lane CF. Tetrahedron  1988,  44:  2763 
• 11c Falorni M. Lardicci L. Giacomelli G. J. Org. Chem.  1986,  51:  5291 
• 11d Brown HC. Lane CF. J. Am. Chem. Soc.  1970,  92:  6660 
• 11e Brown HC. Lane CF.
  J. Chem. Soc. D: Chem. Commun.  1971,  521 
• 11f Lane CF. Brown HC. J. Organomet. Chem.  1971,  26:  C51 
• 11g Tufariello JJ. Hovey MM. J. Chem. Soc. D: Chem. Commun.  1970,  372 
• 11h Kabalka GW. Sastry KAR. Hsu HC. Hylarides MD. J. Org. Chem.  1981,  46:  3113 
• 11i Maruoka K. Sano H. Shinoda K. Nakai S. Yamamoto H. J. Am. Chem. Soc.  1986,  108:  6036 
• 11j Tufariello JJ. Hovey MM. J. Am. Chem. Soc.  1970,  92:  3221 
• 12a Tamao K. Yoshida J. Takahashi M. Yamamoto H. Kakui T. Matsumoto H. Kurita A. Kumada M. J. Am. Chem. Soc.  1978,  100:  290 
• 12b Tamao K. Yoshida J. Yamamoto H. Kakui T. Matsumoto H. Takahashi M. Kurita A. Murata M. Kumada M. Organometallics  1982,  1:  355 
• 13a Hart DW. Schwartz J. J. Am. Chem. Soc.  1974,  96:  8115 
• 13b Tolstikov GA. Miftakhov MS. Valeev FA. Izv. Akad. Nauk SSSR, Ser. Khim.  1979,  2576 
• 14a Isagaga K. Tatsumi K. Otsuji Y. Chem. Lett.  1977,  1117 
• 14b Sato F. Sato S. Kodama H. Sato M. J. Organomet. Chem.  1977,  142:  71 
• 14c Lee H.-S. Kim C.-E. J. Korean Chem. Soc.  2003,  47:  297 
• 14d Lee H.-S. Lee G.-Y. J. Korean Chem. Soc.  2005,  49:  321 
• 14e Gavrilenko VV. Kolesov VS. Zakharkin LI. Izv. Akad. Nauk SSSR, Ser. Khim.  1985,  681 
• 16 For an example of the use of HBr to prepare key substrates for sequential radical reactions, see: Zhang W. Hua Y. Geib SJ. Hoge G. Dowd P. Tetrahedron  1994,  50:  12579 

10

^¹H NMR of the concentrated reaction mixture in entry 6 of Table 1 shows peaks assigned to 2-bromo-2,4,4-trimethyl-pentane as the product, suggesting that hydrogen abstraction from isooctane would occur selectively at the tertiary position of isooctane.

15

The reaction without fluorous phase gave an inferior result. For example, irradiation of a mixture of bromine (1.16 mmol) and isooctane (6 mL) with a 500 W Xe lamp for 30 min, followed by addition of 1-dodecene (1 mmol) at r.t., gave 1-bromododecane in 79% yield together with unreacted 1-dodecene (11%). In this procedure, probably some HBr generated would outgas during the reaction.

17

Typical Procedure for Photoirradiative Phase - Vanishing Hydrogen Bromide Addition to Alkenes (Table 2, entry 2): FC-72 (6 mL) was placed in a Pyrex test tube (13 mm
Æ × 105 mm) to which bromine (2.1 mmol, 340 mg) was added slowly using a glass pipette. Isooctane (1.5 mL) solution of 1-dodecene (2.0 mmol, 340 mg) was then added slowly, forming three layers. The test tube was irradiated with a 500 W Xenon lamp for 2 h. The isooctane layer was taken up with a pipette. Then, additional hexane (4 × 4 mL) was placed on the residual FC-72 layer, followed by decanting off. The combined organic layer was washed with aq 10% Na₂S₂O₃ (30 mL) and sat. brine (30 mL), dried over Na₂SO₄, and concentrated. Purification by a short column chromatography on silica gel with hexane gave 1-bromo-dodecane (480 mg, 96%).