Dramatic Effect of Boron-Based Lewis Acids in Cross-Metathesis Reactions

Abstract

Amino compounds such as allylic carbamates or amides are poor partners in cross-metathesis reactions because of possible coordination of the emerging carbene to the polar functional group. Whereas the use of titanium Lewis acid catalysts was unsatisfactory, an impressive increase in yields was obtained with boron-based Lewis acids.

Key words

cross-metathesis - Lewis acid - amino compounds - boron - ruthenium

References

• 1 Schwab P. France MB. Ziller JW. Grubbs RH. Angew. Chem., Int. Ed. Engl.  1995,  34:  2039 
• 2 Scholl M. Ding S. Lee CW. Grubbs RH. Org. Lett.  1999,  1:  953 
• 3a Kingbury JS. Harrity JPA. Bonitatebus PJ. Hoveyda AH. J. Am. Chem. Soc.  1999,  121:  791 
• 3b Garber SB. Kingsbury JS. Gray BL. Hoveyda AH. J. Am. Chem. Soc.  2000,  122:  8168 
• 3c Gessler S. Randl S. Blechert S. Tetrahedron Lett.  2000,  41:  9973 
• 4 For a recent review, see: Connon SJ. Blechert S. Angew. Chem. Int. Ed.  2003,  42:  1900 
• For examples of problems with allylic carbamates, see:
• 5a Vasbinder MM. Miller SJ. J. Org. Chem.  2002,  67:  6240 
• 5b Biagini SC. Gibson SE. Keen SP. J. Chem. Soc., Perkin Trans. 1  1998,  2485 
• 5c For a recent review, see: Vernall AJ. Abell AD. Aldrichimica Acta  2003,  36:  93 
• 6 Fürstner A. Langemann K. J. Am. Chem. Soc.  1997,  119:  9130 
• 7 The compatibility of boron-derived Lewis (BCl₃) acids has been reported once in an example of tandem RCM enyne-Diels-Alder reactions: Bentz D. Laschat S. Synthesis  2000,  1766 
• Isomerization is currently observed for metathesis of nitrogen derivatives. For recent examples, see:
• 9a Terada Y. Arisawa M. Nishida A. Angew. Chem. Int. Ed.  2004,  43:  4063 
• 9b Chang M.-Y. Hsu R.-T. Tseng T.-W. Sun P.-P. Chang N.-C. Tetrahedron  2004,  60:  5545 

8

Usually CM coupling requires two or three equivalents of one partner. Although use of more than one equivalent of one of the olefin partner slightly improves the yield of the coupling.