Highly diastereoselective 1,3-dipolar cycloaddition of nonstabilized azomethine ylides to 3-nitro-2-trihalomethyl-2H-chromenes: synthesis of 1-benzopyrano[3,4-c]pyrrolidines

Abstract

a b s t r a c tReactions of 3-nitro-2-trifluoro(trichloro)methyl-2H-chromenes, including 2-unsubstituted derivatives, with N-alkyl-a-amino acids (sarcosine, proline) and paraformaldehyde proceed diastereoselectively to give 1-benzopyrano [3,4-c]

Domino reaction of 3-nitro-2-(trifluoromethyl)-2H-chromenes with 2-(1-phenylalkylidene)malononitriles: synthesis of functionalized 6-(trifluoromethyl)-6H-dibenzo[b,d]pyrans and a rare case of [1,5] sigmatropic shift of the nitro group

“…These data were in good agreement with the structure of compounds 7, being constructed via a [1,5] sigmatropic nitro-shift. In addition, the regio-and stereochemistry of 7a and 7b were unambiguously confirmed by single crystal X-ray diffraction analysis (Figs.…”

“…4 1,3-Dipolar cycloaddition of nonstabilised azomethine ylides to these compounds proceeds diastereoselectively to afford 1-benzopyrano [3,4-c]pyrrolidines. 5 Moreover, chromenes 1 undergo heterodiene cycloaddition to 2,3-dihydrofuran and ethyl vinyl ether to give cyclic nitronates with high stereoselectivity and in good yields. 6 The application of this procedure to N-cyclohexenylmorpholine led to the corresponding chromeno [3,4-c][1,2] benzoxazin-6-oxides.…”

“…6 The application of this procedure to N-cyclohexenylmorpholine led to the corresponding chromeno [3,4-c][1,2] benzoxazin-6-oxides. 7 In addition, a two-step formation of 5-(trifluoromethyl)-5H-chromeno [3,4-b]pyridines in moderate yield was achieved by addition of aminoenones derived from acetylacetone and cyclic amines to 2-CF 3 -chromenes 1, followed by acid hydrolysis and subsequent [1,4]-H shift with intramolecular cyclization. 8 On the other hand, the dibenzo [b,d]pyran system constitutes the skeleton of a number of physiologically active natural products and drugs, such as cannabinol, and its derivatives have attracted strong interest due to their useful biological and pharmacological properties.…”

“…It is likely that this nitro-shift reflects a greater electronic repulsion between the neighbouring CF 3 and NO 2 groups in 6 than that between the Ar and NO 2 in 5, the consequence being that the trifluoromethyl group and the nitro group are forced to be further apart. Previous reports of [1,5] and [1,3] sigmatropic nitro-shifts are rare and all involve shifts from a tertiary carbon atom to a carbon bearing a hydrogen in a series of adducts from ipso-nitration.…”

1,3-Dipolar Cycloaddition Reactions of Azomethine Ylides with Carbonyl Dipolarophiles Yielding Oxazolidine Derivatives

“…This work was predicated on the observation that sarcosine (47), paraformaldehyde (2m) and pyrone aldehyde 2o reacted to form N-methyloxazolidine 84 [84]. Azomethine ylide 81, formed in this way, also underwent cycloaddition reactions with 2-chloro-3-quinolinecarboxaldehydes to afford the corresponding 3-quinolyl-1,3-oxazolones [85], and in an internal competition reaction with 3-formyl-2H-chromene to furnish a 2.8:1 mixture of the corresponding benzo [3,4-c]pyrrolidine and oxazolidine cycloadducts, respectively [86]. The non-stabilized azomethine ylide 81, derived in situ from sarcosine (47) and paraformaldehyde (2m), underwent 1,3-dipolar cycloaddition reactions with various aromatic aldehydes 2 to form the corresponding 5-aryl-3-methyloxazolidines 82 (Scheme 19, Table 11).…”