Diels−Alder Cycloadditions of Ethyl 2-Carbomethoxyethenesulfinates with Cyclopentadiene. Lewis Acid Enhancement and Adduct Identification with the Assistance of Competitive Stereodifferentiating Iodolactonization and Iodosultinization Reactions

Abstract

Ethyl (Z)-2-carbomethoxyethenesulfinate (1) and ethyl (E)-2-carbomethoxyethenesulfinate (2) were each subjected to cyclopentadiene (ca. 3 equiv) in order to determine their reactivity in Diels-Alder reactions. Thermal reactions proceeded in less than 4 h, while Lewis Acid enhanced reactions were substantially faster and demonstrated greater selectivity. In particular, the BF(3).Et(2)O-mediated cycloaddition of 1 gave syn/endo cycloadduct 3a as a major diastereomer in about 90% yield. The reactions of 2 were less synthetically useful. The structures of the cycloadducts were established through a combination of X-ray crystal structure determinations and through exposure of the compounds to an electrophilic iodine reagent. Each cycloadduct underwent an iodocyclization reaction with either the carboxylic ester or the sulfinate ester participating in the formation of a polycyclic lactone or sultine, respectively. The iodocyclization reactions allowed further elucidation of the cycloadduct structures.

Evaluation of ethyl 2-carbomethoxyethenesulfinates as 2-hydroxymethyl enethiol equivalents in the Diels–Alder reaction

“…Among the numerous Lewis acids tried, 30 Et 2 AlCl, ZnCl 2 and ZnBr 2 were found to be most generally applicable. A summary of the results is shown in Table 1.…”

“…29 The Schwan group introduced Z-and E-ethyl 2-carbomethoxyethenesulfinates 1 and 2 as dieneophiles in the thermal and Lewis acid accelerated Diels-Alder reactions with cyclopentadiene. 30 The various isomeric cycloadducts obtained in that investigation were identified with the assistance of X-ray crystallography and electrophilic cyclization chemistry. The advantage of the sulfinate functionality over sulfones and sulfoxides is its potential for facile conversion to thiol in a single reduction step.…”

Unexpected reactions of Grignard reagents with selected β-carboalkoxy substituted sulfinate esters

“…[28][29][30][31] Diels-Alder reactions with sulfinate ester-bearing dienophiles have also been studied. [32][33][34][35] The sulfinate is particularly appealing for its ability to be readily adapted by reduction, 34,36,37 oxidation, [38][39][40] and transformation to sulfoxide. [41][42][43] Moreover, we have demonstrated that appropriately disposed sulfinate esters can participate in iodosultinization reactions with inversion of sulfinyl configuration.…”

“…[41][42][43] Moreover, we have demonstrated that appropriately disposed sulfinate esters can participate in iodosultinization reactions with inversion of sulfinyl configuration. 32 In the current study, we examined the Grignard substitution chemistry of a series of Diels-Alder cycloadducts previously prepared from dienophile 1. 32,34 The cycloadducts bear sulfinate and carboxylate esters on vicinal carbons.…”

Determination of theZ1H NMR chemical shift substituent parameters for the sulfinyl chloride and sulfinate ester functionalities

“…Sulfinyl chloride and sulfinate ester functional groups are part of modern investigations [9,10] and, as such, double bonded compounds bearing these substituents are of interest to us [11][12][13][14][15][16] and to others [17][18][19][20][21][22][23][24][25][26][27]. Unfortunately the alkene additivity rule is unavailable for investigators in this area due to the lack of appropriate substituent constants.…”