A Novel, Efficient, and Highly Selective O-Bn Bond Cleavage Reaction via a Rare K-Induced Electron Transfer Process

Abstract

A new, efficient and highly selective deprotective method of both benzyl and benzylidene groups for protection of monohydroxyl and dihydroxyl, respectively, has been developed by using the system K-t-BuNH₂-t-BuOH-18-crown-6. This method is valuable since it can not only selectively protect the TBDMS and THP groups and the ethylene ketal from cleavage, but also keep the separate or conjugated C=C bonds from reduction. A possible electron transfer reaction process was also suggested.

Key words

selective - benzyl - benzylidene - potassium - electron transfer

References

• 1a Heathcock CH. Ratcliffe R. J. Am. Chem. Soc.  1971,  93:  1746 
• 1b Hartung WH. Simonoff R. Org. React.  1953,  7:  263 
• 1c Bieg T. Szeja W. Carbohydr. Res.  1985,  140:  C7 
• 2a McCloskey CM. Adv. Carbohydr. Chem.  1957,  12:  137 
• 2b Schön I. Chem. Rev.  1984,  84:  287 
• 2c Zaoral M. Jezek J. Straka R. Masek K. Collect. Czech. Chem. Commun.  1978,  43:  1797 
• 3a Angibeaud P. Defaye J. Gadelle A. Utille J.-P. Synthesis  1985,  1123 
• 3b Deslongchamps P. Moreau C. Fréhel D. Hênevert R. Can. J. Chem.  1975,  53:  1204 
• 4a Hori H. Nishida Y. Ohrui H. Meguro H. J. Org. Chem.  1989,  54:  1346 
• 4b Park MH. Takeda R. Nakanishi K. Tetrahedron. Lett.  1987,  28:  3823 
• 5a Mairanvsky VG. Angew. Chem., Int. Ed. Engl.  1976,  15:  281 
• 5b Mayeda EA. Miller LL. Wolf JF. J. Am. Chem. Soc.  1972,  94:  6812 
• 5c Schemidt W. Steckhan E. Angew. Chem., Int. Ed. Engl.  1979,  18:  801 
• 6 Xia WJ. Li DR. Shi L. Tu YQ. Tetrahedron. Lett.  2002,  43:  627 
• 8 Tu YQ. Sun LD. Wang PZ. J. Org. Chem.  1999,  64:  629 
• 9 Crimmins MT. Hollis WG. Lever GJ. Tetrahedron Lett.  1987,  28:  3647 
• 10 Bieg T. Szeja W. Synthesis  1986,  317 
• 11 Takano S. Akiyama M. Sato S. Ogasawara K. Chem. Lett.  1983,  1593 
• 12 Szarek WA. Zamojski A. Tiwari KN. Ison ER. Tetrahedron. Lett.  1986,  27:  3827 
• 13 Barrett AGM. Prokopiou PA. Barton DHR. Boar RB. McGhie JF. J. Chem. Soc., Chem. Commun.  1979,  1173 
• 14 Organic Chemistry   6th ed.:  Solomons TWG. John Wiley and Sons Inc.; New York: 1996.  p.460 

7

One equiv of substrate dissolved in dried THF was sequentially added to two equiv of dry t-BuNH₂ and two equiv of t-BuOH and 10 equiv of potassium and 0.1 equiv of 18-crown-6. The mixture was stirred at r.t. for 1-6 h (the starting material disappeared, checked with TLC), workup as the general procedure to afford the corresponding alcohols in 73-99% yield.