Tandem dinucleophilic cyclization of cyclohexane-1,3-diones with pyridinium salts

Abstract

SummaryThe cyclization of cyclohexane-1,3-diones with various substituted pyridinium salts afforded functionalized 8-oxa-10-aza-tricyclo[7.3.1.02,7]trideca-2(7),11-dienes. The reaction proceeds by regioselective attack of the central carbon atom of the 1,3-dicarbonyl unit to 4-position of the pyridinium salt and subsequent cyclization by base-assisted proton migration and nucleophilic addition of the oxygen atom to the 2-position, as was elucidated by DFT computations. Fairly extensive screening of bases and additives revealed that the presence of potassium cations is essential for formation of the product.

Adventures in the Chemistry of Multicomponent and Domino Reactions

“…The cyclization of cyclohexane-1,3-dione ( 21 ). [19] The cyclization proceeds by attack of the central carbon atom of 21 b,c to carbon C-4 of the pyridinium ion and cyclization by attack of the oxygen atom to carbon C-6. The regioselectivity of the cyclization of 21 b,c with ester-substituted pyridinium salts 43 a-f is different from that observed for the corresponding cyclizations of 43 a-f with thioxindoles 1 a-c.…”

“…The cyclization of cyclohexane-1,3-diones 21 b,c with 2cyanopyridinium salts 47 a-c afforded products 50 a-f (Scheme 20). [19] The cyclization again proceeds by attack of the…”

“…The cyclization of cyclohexane‐1,3‐dione ( 21 c ) and dimedone ( 21 b ) with 3‐acylpyridinium salts 43 a – f and 3‐cyanopyridinium salts 45 a – f , again investigated by Mostafa, afforded 8‐oxa‐10‐aza‐tricyclo[7.3.1.02,7]trideca‐2(7),11‐dienes 49 a – x (Scheme 19). [19] The cyclization proceeds by attack of the central carbon atom of 21 b,c to carbon C‐4 of the pyridinium ion and cyclization by attack of the oxygen atom to carbon C‐6. The regioselectivity of the cyclization of 21 b,c with ester‐substituted pyridinium salts 43 a – f is different from that observed for the corresponding cyclizations of 43 a – f with thioxindoles 1 a – c .…”

“…The cyclization of cyclohexane‐1,3‐diones 21 b,c with 2‐cyanopyridinium salts 47 a – c afforded products 50 a – f (Scheme 20). [19] The cyclization again proceeds by attack of the central carbon atom of 21 b,c to carbon C‐4 of the pyridinium ion and cyclization via carbon C‐6. The regioselectivity of the cyclization of 47 a – c with 21 b,c is identical to the one observed for the corresponding reaction of 47 a – c with thioxindoles 1 a – c and can be explained by steric reasons.…”