Carbonyl sulfide 2+2 cycloaddition reactions

Hydroxy-THISs react with electron-deficient alkynes to give nonisol-able adducts that extrude carbonyl sulfide, affording pyrroles (23). Compound 16 (X = 0) seems particularly reactive (Scheme 16) (25). The cycloaddition to benzyne yields isoindoles in low- yield. Further cyclo-addition between isoindole and benzyne leads to an iminoanthracene as the main product (Scheme 17). The cycloadducts derived from electron-deficient alkenes are stable (23, 25) unless highly strained. Thus the two adducts, 18a (R = H, R = COOMe) and 18b (R = COOMe, R = H), formed from 7, both extrude furan and COS under the reaction conditions producing the pyrroles (19. R = H or COOMe) (Scheme 18). Similarly, the cycloadduct formed between 16 (X = 0) and dimethylfumarate... 

The Diels-Alder cycloaddition potential of fused 4-aryldihydropyrimidine mesomeric betaines has been studied. The cross-conjugated thiazinium betaine 317 underwent 1,4-dipolar cycloaddition with electron-rich dipolaro-philes, and thus 1-diethylaminoprop-l-ine gave the pyrido[l,2-tf]pyrimidine 318 by loss of carbonyl sulfide (Equation 34). Reaction of 317b with 1,1-diethoxyethene resulted in the 8-ethoxy analogue of 318 (R = H) <1997JOC3109>. 

The meso-ionic l,3-dithiol-4-ones (134) participate - in 1,3-dipolar cycloaddition reactions giving adducts of the general type 136. They show a remarkable degree of reactivity toward simple alkenes including tetramethylethylene, cyclopentene, norbomene, and norbor-nadiene as well as toward the more reactive 1,3-dipolarophilic olefins dimethyl maleate, dimethyl fumarate, methyl cinnamate, diben-zoylethylene, A -phenylmaleimide, and acenaphthylene. Alkynes such as dimethyl acetylenedicarboxylate also add to meso-ionic 1,3-dithiol-4-ones (134), but the intermediate cycloadducts are not isolable they eliminate carbonyl sulfide and yield thiophenes (137) directly. - ... 

Among the carbonylative cycloaddition reactions, the Pauson-Khand (P-K) reaction, in which an alkyne, an alkene, and carbon monoxide are condensed in a formal [2+2+1] cycloaddition to form cyclopentenones, has attracted considerable attention [3]. Significant progress in this reaction has been made in this decade. In the past, a stoichiometric amount of Co2(CO)8 was used as the source of CO. Various additive promoters, such as amines, amine N-oxides, phosphanes, ethers, and sulfides, have been developed thus far for a stoichiometric P-K reaction to proceed under milder reaction conditions. Other transition-metal carbonyl complexes, such as Fe(CO)4(acetone), W(CO)5(tetrahydrofuran), W(CO)5F, Cp2Mo2(CO)4, where Cp is cyclopentadienyl, and Mo(CO)6, are also used as the source of CO in place of Co2(CO)8. There has been significant interest in developing catalytic variants of the P-K reaction. Rautenstrauch et al. [4] reported the first catalytic P-K reaction in which alkenes are limited to reactive alkenes, such as ethylene and norbornene. Since 1994 when Jeong et al. [5] reported the first catalytic intramolecular P-K reaction, most attention has been focused on the modification of the cobalt catalytic system [3]. Recently, other transition-metal complexes, such as Ti [6], Rh [7], and Ir complexes [8], have been found to be active for intramolecular P-K reactions. 

As reported before (see Section 4.14.6.1, Scheme 19), thermolysis of oxathiazolines (169) proceeds via a retro 1,3-dipolar cycloaddition to produce the carbonyl compound and the nitrile sulfide intermediate. Trapping reactions have been carried out with DMAD, ECF (ethyl cyano formate), and benzonitrile to give respectively isothiazoles (170) and thiadiazoles (171) and (172). However in two particular cases (R = 4-MeOC6H4, 4-ClCgH4, thermolysis in the presence of benzonitrile gives (172) and the thiadiazole (173) in very low yields. It has been suggested that the latter arises... 

Reaction with thiocarbonyl compounds. The thiocarbonyl compounds obtained by photochemical oxidation of phenacyl sulfides can be trapped efficiently by a 1,3-dipolar cycloaddition with 1 to give 2. This heterocycle can be cleaved to carbonyl compounds by Bu4N F or (CjH5)3N HF. This process is more efficient and more general than photolysis of phenacyl sulfides in the presence of oxygen. 

Alkenyl sulfides are known to react with some labile electron-deficient olefins such as methyl vinyl ketone in the presence of AlCl3 to form cyclobutanes [25]. In the present chiral titanium-promoted asymmetric reaction, alkenyl sulfides can also be employed as electron-rich components. 2-Ethylthio-l-propene (7a) reacts with 2a in the presence of a catalytic amount of the chiral titanium reagent, giving the diastereomeric [2-1-2] cycloaddition products 8a and 9a in 51% (>98% ee) and 19% (79% ee) yields, respectively (Scheme 7 and Table 2). Although 2-ethylthio-l-propene (7a) is known as a good ene component in the reaction with carbonyl compounds, 3-(3-(methoxycarbonyl)-5-ethylthio-5-hex-enoyl)-l,3-oxazolidin-2-one, an ene product, is obtained only in 16% yield as a side product. 

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