Lewis Super‐Acid Catalyzed Cyclizations: A New Route to Fragrance Compounds

Abstract

This review deals with the application of Lewis super acids such as Al(III), In(III), and Sn(IV) triflates and triflimidates as catalysts in the synthesis of fragrance materials. Novel catalytic reactions involving C-C and C-heteroatom bond-forming reactions, as well as cycloisomerization processes are presented. In particular, Sn(IV) and Al(III) triflates were employed as catalysts in the selective cyclization of unsaturated alcohols to cyclic ethers, as well as in the cyclization of unsaturated carboxylic acids to lactones. The addition of thiols and thioacids to non-activated olefins, both in intra- and intermolecular versions, was efficiently catalyzed by In(III) derivatives. Sn(IV) Triflimidates catalyzed the cycloisomerization of highly substituted 1,6-dienes to gem-dimethyl-substituted cyclohexanes bearing an isopropylidene substituent. The hydroformylation of these unsaturated substrates, catalyzed by a Rh(I) complex with a bulky phosphite ligand, selectively afforded the corresponding linear aldehydes. The olfactory evaluation of selected heterocycles, carbocycles, and aldehydes synthesized is also discussed.

Preparation and olfactory evaluation of mono‐ and bicyclic compounds featuring gem‐dimethylcyclohexane structures

“…Bi(OTf) 3 and the salts and reagents were purchased from Aldrich and used as received. Preparation and characterization of products 1 , 12 , 13 , 16 , 17 , 20 and 21 have been previously described …”

“…We have reported the selective cyclization of highly substituted 1,6‐dienes in the presence of a catalytic amount of tin(IV) triflimide, Sn(NTf 2 ) 4 (Tf = CF 3 SO 2 ) . Interestingly, these cyclizations afforded cyclohexane structures, instead of five‐membered rings, generally obtained by catalysis with transition‐metal complexes …”

Aluminium Triflate Catalysed Cyclisation of Unsaturated Alcohols: Novel Synthesis of Rose Oxide and Analogues

“…The high activity of the metallic triflate catalysts is due to the strongly electron-withdrawing trifluoromethanesulfonate group. [9] Pursuing the development of the cycloisomerisation of unsaturated alcohols involving the use of metallic trifluoromethanesulfonates as Lewis "superacid" catalysts, [10] we describe here some novel examples of this catalytic methodology applied to the synthesis of racemic cyclic ethers of the rose oxide family, such as compounds 1-5 (Scheme 1).…”

Synthesis and odour evaluation of allenic derivatives

“…One of the main research interests of our group is the development of novel synthetic methodologies with applications in the flavour and fragrance field . We have been recently interested in the transformation of allenic derivatives into polycyclic compounds .…”