Sequential Diels–Alder/[3,3]-sigmatropic rearrangement reactions of β-nitrostyrene with 3-methyl-1,3-pentadiene

Abstract

SummaryThe tin(IV)-catalyzed reaction of β-nitrostyrene with (E)-3-methyl-1,3-pentadiene in toluene afforded two major nitronic ester cycloadducts in 27% and 29% yield that arise from the reaction at the less substituted diene double bond. Also present were four cycloadducts from the reaction at the higher substituted diene double bond, two of which were the formal cycloadducts of (Z)-3-methyl-1,3-pentadiene. A Friedel–Crafts alkylation product from the reaction of the diene, β-nitrostyrene, and toluene was also obtained in 10% yield. The tin(IV)-catalyzed reaction of β-nitrostyrene with (Z)-3-methyl-1,3-pentadiene in dichloromethane afforded four nitronic ester cycloadducts all derived from the reaction at the higher substituted double bond. One cycloadduct was isolated in 45% yield and two others are formal adducts of the E-isomer of the diene. The product formation in these reactions is consistent with a stepwise mechanism involving a zwitterionic intermediate. The initially isolated nitronic ester cycloadducts underwent tin(IV)-catalyzed interconversion, presumably via zwitterion intermediates. Cycloadducts derived from the reaction at the less substituted double bond of (E)-3-methyl-1,3-pentadiene underwent a [3,3]-sigmatropic rearrangement on heating to afford 4-nitrocyclohexenes. Cycloadducts derived from the reaction at the higher substituted diene double bond of either diene failed to undergo a thermal rearrangement. Rates and success of the rearrangement are consistent with a concerted mechanism possessing a dipolar transition state. An initial assessment of substituent effects on the rearrangement process is presented.

Mechanistic aspects of the synthesis of seven‐membered internal nitronates via stepwise [4 + 3] cycloaddition involving conjugated nitroalkenes: Molecular Electron Density Theory computational study

“…For example, the reactions of 2‐arylnitroethenes with cyclopentadiene is catalyzed by SnCl 4 (Scheme 3). 8 …”

Nitration reactions of conjugated compounds employing lithium nitrate and trifluoroacetic anhydride

“…Also, nitration of 1c affords a high preference for E-isomeric products (only 2% yield of 6 is obtained) despite the starting 1c diene mixture. This is in contrast with other reactions of the 1c diene mixture, for example catalytic Diels-Alder cycloaddition using ␤-nitrostyrene, 13 where regioselectivity is low.…”

“…The crude product was purified by flash chromatography. The most mobile product (eluted with 30:70 EtOAchexanes) amounted to 0.68 g (2.9 mmol, 57% yield) of (E)-N-(2,3dimethyl-4-nitrobut-2-enyl)-N-nitroacetamide (2b): mp 26-28°C; IR 1717 (C=O), 1548, 1370 cm −1 (2 NO 2 ); 1 H NMR ␦ 4.99 (s, 2H), 4.88 (s, 2H), 2.68 (s, 3H), 1.97 (s, 3H), 1.73 (s, 3H); 13…”

“…The cold reaction mixture was stirred for 12 h and worked up (50 mL water and three 50 mL portions of CH 2 Cl 2 ) following the general procedure. The crude product was purified by flash chromatography (50:50 EtOAchexanes) furnishing 0.85 g (52% yield) of N-nitropyrrolidine (23) as a white crystalline solid: mp 57-58°C (lit 10 mp 56-57°C); IR 1498, 1285 cm −1 (N-NO 2 ); 1 H NMR ␦ 3.87 (m, 4H), 2.05 (m, 4H); 13…”

Understanding the Molecular Mechanism of the Rearrangement of Internal Nitronic Ester into Nitronorbornene in Light of the MEDT Study

“…Wade and co-workers proved that the rearrangement of O-allyl nitronic esters (nitronates) obtained in the E-2-phenylnitroethylene and 1,3-cyclohexadiene reaction undergo conversion to the DA product, the γ,δ-unsaturated nitro compound, with high efficiency [10,11]. The necessary nitronic ester precursors are readily obtained by HDA cycloaddition reactions of nitroalkenes with appropriate dienes [10,11,12].…”