Functionalized Imides by Regioselective Ozonation

Abstract

Ozonations of alkoxy-and (acyloxy)-substituted alkylidene-lactams 1 and 5 or of the alkylidene-sultams 9 and 10 proceeded by regioselective cleavage of the exocyclic C=C bonds (Schemes 1 and 2). These bonds are part of an enamide system and, therefore, possess considerable polarity as shown by 13 C-NMR spectra. As a result, the partly known maleimides 3 and 6 or the sulfonimides 11 were obtained. Compounds 3 and 11 reacted with diazomethane to give the highly reactive bicyclic derivatives 8 and 12, respectively. The cinnamylidene-lactames 16a,b were converted by selective ozonolysis mainly into the formylmethylene lactames 17a,b (Scheme 3). The amino-substituted aldehyde 20 bears a structural relationship to the lactone antibiotic basidalin 21a. The tendency of some donor-substituted maleimides to undergo [2 + 2] cycloadditions was assessed (Scheme 4). The configuration of the photodimers 22a,b and 24a,b was established by X-ray crystallography.Introduction. -The cleavage of alkene C=C bonds by ozone to give aldehydes, ketones, and carboxylic acids was introduced into organic chemistry at the beginning of the 20 th century by Harries [1]. Ozonolyses take place under extremely mild reaction conditions and often with excellent yields. The individual course of an ozonization, however, is strongly dependent on the constitution of the starting material, the solvent, and the choice of reductive or oxidative workup conditions (for a comprehensive review, see [2]).A basic three-step mechanism was formulated by Criegee and is now bearing his name [3]. In a sequence of concerted 1,3-dipolar cycloaddition and cycloreversion, carbonyl oxides [4] are formed which are captured by internally generated carbonyl compounds in another 1,3-dipolar cycloaddition to yield ozonides. As a result, for unsymmetrical alkenes, substituent rules for the regioselective OÀO splitting in the cycloreversion step have been formulated [5] [6]. There are, however, exceptions from these rules, and the ozonide-forming step may be bypassed due to low dipolarophilicity of the carbonyl intermediate. Both is examplified in the ozonolysis of ketene acetals [7]. Modifications of the original Criegee mechanism have been introduced later [8]. An alternative mechanistic concept of ozonations was recently brought up for discussion [9]. According to the donor-acceptor concept, ozonations are regarded as oxidation reactions with radical-ion intermediates.It is well known that the C=C bond of enol ethers is readily cleaved by ozone forming a carbonyl compound and a carboxylic acid ester [10 -14]. Analogously, in the ozonolysis of enol esters, beside a carbonyl compound, a mixed carboxylic acid anhydride is

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Ruthenium-Catalyzed Selective Hydrogenation of bis-Arylidene Tetramic Acids. Application to the Synthesis of Novel Structurally Diverse Pyrrolidine-2,4-diones

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Total Synthesis of the Antitumor Antibiotic Basidalin

“…[6][7][8][9][10] However, while certain analogues have succumbed to synthesis (e.g. 2-4, Figure 1), [7][8][9] basidalin itself has so far proven remarkably elusive.…”

“…[6][7][8][9][10] However, while certain analogues have succumbed to synthesis (e.g. 2-4, Figure 1), [7][8][9] basidalin itself has so far proven remarkably elusive. 6,7,10 Thus, Hiyama's advanced intermediates 5 and 6 (Scheme 1), each synthesized in five steps, failed to undergo conversion to 1 under an extensive array of conditions.…”