Zinc Perchlorate Hexahydrate Catalysed Conjugate Addition of Thiols to α,β-Unsaturated Ketones

Abstract

Zn(II) perchlorate hexahydrate has been found to be a new and efficient catalyst for conjugate addition of thiols to α,β-unsaturated ketones under solvent-free conditions at room temperature. The reaction of aryl, arylalkyl and alkyl thiols with cyclic and acyclic α,β-unsaturated ketones takes place affording excellent yields after five minutes to six hours. The compatibility of Zn(ClO₄)₂·6H₂O with different solvents provides a means to carry out the reaction under versatile experimental conditions. The rate of thiol addition was dependent on the electronic and steric factors of the enones and the thiols. The substituent at the β-carbon of the α,β-unsaturated ketone substrate caused steric hindrance during conjugate addition and required longer reaction times. The rate of reaction for alkane thiols e.g. ethanethiol was sluggish compared to that of aryl thiols.

Keywords

conjugate addition - thiol - α,β-unsaturated ketone - zinc(II) perchlorate - catalyst

References

• 1 Fujita E. Nagao Y. Bioorg. Chem.  1977,  6:  287 
• 2a Fluharty AL. In The Chemistry of the Thiol Group   Patai S. Wiley Interscience; New York: 1974.  Part 2.. p.589 
• 2b Trost BM. Keeley DE. J. Org. Chem.  1975,  40:  2013 
• 2c Kumar A. Salunkhe RV. Rane RA. Dike SY. J. Chem. Soc., Chem. Commun.  1991,  485 
• 3 Cohen T. Mura AJ. Shull DW. Fogel ER. Ruffner RJ. Falck JR. J. Org. Chem.  1976,  41:  3218 
• 4 Bakuzia P. Bakuzis MLF. J. Org. Chem.  1981,  46:  235 
• 5 Cherkauskas JP. Cohen T. J. Org. Chem.  1992,  57:  6 
• 6a CdI₂: Saito M. Nakajima M. Hashimoto S. Tetrahedron  2000,  56:  9589 
• 6b InBr₃: Bandini M. Cozzi PG. Giacomini M. Melchiorre P. Selva S. Umani-Ronchi A. J. Org. Chem.  2002,  67:  3700 
• 6c InCl₃: Ranu BC. Dey SS. Samanta S. ARKIVOC  2005,  iii:  44 
• 7 Srivastava N. Banik BK. J. Org. Chem.  2003,  68:  2109 
• 8a Zahouily M. Abrouki Y. Rayadh A. Tetrahedron Lett.  2002,  43:  7729 
• 8b Abrouki Y. Zahouily M. Rayadh A. Bahlaouan B. Sebti S. Tetrahedron Lett.  2002,  43:  8951 
• 9a Hf(OTf)₃: Kobyashi S. Ogawa C. Kawamura M. Sugiura M. Synlett  2001,  983 
• 9b Bi(OTf)₃: Alam MM. Varala R. Adapa SR. Tetrahedron Lett.  2003,  44:  5115 
• 10a Zeolites: Sreekumar R. Rugmini P. Padmakumar R. Tetrahedron Lett.  1997,  38:  6557 
• 10b Al₂O₃: Cheng S. Comer DD. Tetrahedron Lett.  2002,  43:  1179 
• 10c Nafion^® SAC-13: Wabnitz TC. Yu J.-Q. Spencer JB. Synlett  2003,  1070 
• 11a Yadav JS. Reddy BVS. Baishya G. J. Org. Chem.  2003,  68:  7098 
• 11b Ranu BC. Dey SS. Hajra A. Tetrahedron  2003,  59:  2417 
• 11c Ranu BC. Dey SS. Tetrahedron  2004,  60:  4183 
• 12 Olah GA. Prakash GKS. Superacids   Wiley; New York: 1985. 
• 13a BiOClO₄: Chakraborti AK. Gulhane R. Shivani . Synthesis  2003,  1805 
• 13b Zn(ClO₄)₂: Bartoli G. Bosco M. Dalpozzo R. Marcantoni E. Massaccesi M. Sambri L. Eur. J. Org. Chem.  2003,  4611 
• 13c Mg(ClO₄)₂: Chakraborti AK. Sharma L. Gulhane R. Shivani . Tetrahedron  2003,  59:  7661 
• 13d Mg(ClO₄)₂: Bartoli G. Bosco M. Dalpozzo R. Marcantoni E. Massaccesi M. Rinaldi S. Sambri L. Synlett  2003,  39 
• 13e LiClO₄: Nakae Y. Kusaki I. Sato T. Synlett  2001,  1584 
• 14 Huhey JE. Inorganic Chemistry: Principles of Structure and Reactivity   3rd ed.:  Harper & Row; Singapore: 1990.  Chap. 7.
• 15 Casachi A. Desimoni G. Faita G. Invernizzi AG. Lanati S. Righetti P. J. Am. Chem. Soc.  1993,  115:  8002 
• 16 Yatsimirskii KB. Vasil’ev VP. Instability Constants of Complex Compounds   Pergamon; Elmsford N. Y.: 1960. 
• 17 Garrett RL. In Designing Safer Chemicals, In American Chemical Society Symposium Series 640   Chap. 1:  Garrett RL. De Vito SC. ACS; Washington DC: 1996.