Synthesis of 3,4-Bis(benzylidene)cyclobutenes

Abstract

The syntheses of several derivatives of 3,4-bis(benzylidene)cyclobutene are reported. Previously unknown 1,2-dibromo-3,4-bis(benzylidene)cyclobutene was obtained through in situ generation of 1,6-diphenyl-3,4-dibromo-1,2,4,5-tetraene followed by electrocyclic ring closure. Ensuing reduction and metal-catalyzed cross-coupling provided additional derivatives. The effects of ring strain on the geometry and electronics of these derivatives were examined by X-ray crystallography and ^¹H NMR spectroscopy, respectively.

electrocyclic reactions - ring closure - allenes - highly strained ring systems - metal-catalyzed cross-coupling

References and Notes

1 Blomquist AT. Maitlis PM. Proc. Chem. Soc. (London)  1961,  332 

2a Huntsman WD. Wristers HJ. J. Am. Chem. Soc.  1963,  85:  3308 

2b Huntsman WD. Wristers HJ. J. Am. Chem. Soc.  1965,  89:  342 

2c Coller BAW. Heffernan ML. Jones AJ. Aust. J. Chem.  1968,  21:  1807 

2d Hopf H. Angew. Chem., Int. Ed. Engl.  1970,  9:  732 

3 Toda F. Garratt P. Chem. Rev.  1992,  92:  1685 

4 Braverman S. Suresh Kumar EVK. Cherkinsky M. Sprecher M. Goldberg I. Tetrahedron  2005,  61:  3547 

For examples of the use of 2, see:

5a Toda F. Akagi K.
J. Chem. Soc., Chem. Commun.  1970,  764 

5b Toda F. Akagi K. Tetrahedron  1971,  27:  2801 

5c Iyoda M. Kuwatami Y. Oda M. J. Am. Chem. Soc.  1989,  111:  3761 

5d Toda F. Tanaka K. Sano I. Isozaki T. Angew. Chem.  1994,  106:  1856 

5e Kuwatani Y. Yamamato G. Iyoda M. Org. Lett.  2003,  5:  3371 

5f Kuwatani Y. Yamamoto G. Oda M. Iyoda M. Bull. Chem. Soc. Jpn.  2003,  5:  2188 

6 Toda F. Kumada K. Ishiguro N. Akagi K. Bull. Chem. Soc. Jpn.  1970,  43:  3535 

7 Toda F. J. Chem. Soc., Chem. Commun.  1969,  1219 

8 Brandsma L. Synthesis of Acetylenes, Allenes and Cumulenes   Elsevier; Oxford: 2004.  p.235-265  

9a Ulman A. Manassen J. J. Am. Chem. Soc.  1975,  97:  6540 

9b Smith CD. Tchabanenko K. Adlington RM. Baldwin JE. Tetrahedron Lett.  2006,  47:  3209 

10 Landor SR. Demetriou B. Evans RJ. Grzeskowiak R. Devey P. J. Chem. Soc., Perkin Trans. 2  1972,  1995 

11 Jacobs TL. Brill WF. J. Am. Chem. Soc.  1953,  75:  1314 

12a Kleveland K. Skattebøl L. J. Chem. Soc., Chem. Commun.  1973,  432 

12b Pasto DJ. Yang S.-H. J. Org. Chem.  1989,  54:  3544 

13

Dibromide 6 was found to rearrange to 5 (ca. 50%) and hydrolyze to 4 (ca. 50%) upon chromatography on silica gel and decomposed partially during recrystallization attempts.

14 Toda F. Tanaka K. Tamashima T. Kato M. Angew. Chem. Int. Ed.  1998,  37:  2724 

15 The distribution of isomers was determined by ^¹H NMR

16

Photolysis experiments were conducted in hexane using a Hg pen-lamp, without the use of optical filters.

17

Spartan B3LYP/6-31+g*, relative E (kcal/mol): 7 (in,out) = -0.4487, 7 (in,in) = 0, 7 (out,out) = 0.0056.

18 Pasto DJ. Kong W. J. Org. Chem.  1989,  54:  4028 

19

Attempts to purify compound 8 via column chromatography or recrystallization were unsuccessful due to its limited stability. Any impurities visible in Figure S1 are believed to be primarily high-molecular-weight decomposition products.

20 Roberts BW. Wissner A. J. Am. Chem Soc.  1972,  94:  7168 

For examples of this methodology in the synthesis of polycyclic aromatic compounds, see:

21a Tovar JD. Swager TM. Adv. Mater.  2001,  13:  1775 

21b Tovar JD. Rose A. Swager TM. J. Am. Chem. Soc.  2002,  124:  7762