1,4-Oxathiin oxide

Various 1,4-oxathiins have been converted to the sulfoxides in a highly stereoselective reaction. The sulfoxides undergo a thermal retro-Diels-Alder reaction to ot,a -dioxosulrines which can behave both as electron deficient dienes and as dienophiles, affording different oxathiins and dihydrothiopyran 1-oxides, respectively <96T12233>. In like manner, o-thioquinone 5-oxides have been generated and they too exhibit diene and dienophile behaviour <96T12247>. 

Oxathiine derivatives lb 301,304 Oxathizine fungicides la 44 Oxazepam la 364 Oxazolidinthione derivatives lb 301 Oxeladine citrate lb 327 Oxidation, aluminium isopropoxide la 59 -, atmospheric oxygen la 60 -, chromic acid la 59, 60 -, hydrogen peroxide la 59 -, iodine la 60... 

The desulfurization pathway was proposed to be BT -> BT sulfone -> benzo[e][l,2]oxanthiin S-oxide -> o-hydroxystyrene. Additionally, formation of the intermediate benzo(e)(l,2)oxathiin S,S dioxide was inferred to a side pathway resulting in formation of benzofuran as shown in Fig. 7. This pathway is similar to that reported for Sinorhizobium KT55, Paenibacillus sp. strain All-2 and R. erythropolis KT462. 

Langa et al. [67] described the microwave-induced Diels-Alder reaction of o-quino-dimethane, generated in situ from 4,5-benzo-3,6-dihydro-l,2-oxathiin-2-oxide (74) (sultine), [68, 69] leading to cycloadduct 75 (Scheme 9.21). This reaction was the first application of microwave irradiation to the preparation of a functionalized C60 [67]. 

At low temperature and in the presence of catalyst, simple conjugated dienes add SO2 reversibly via hetero-Diels-Alder addition and generate 3,6-dihydro-l,2-oxathiine 2-oxides 8 (sultines) <1992JA9210, 1993TL6269,... 

The aminolysis of dibenzo[l,2]oxathiin 6-oxide 10 with primary and secondary amines in water was quantitively followed by the absorption at 270 nm in UV spectroscopy, from which the reaction was found to obey pseudo-first-order kinetics < 1999TL8901 >. Because of the lack of a distinct difference in the magnitude of y obs between primary and secondary amines, and between acyclic and cyclic amines, the aminolysis reaction must proceed in two steps the first is a fast formation of intermediate 102 followed by a second slow decomposition step to the reaction product 103 (Scheme 24). 

Sultones react easily with amines and anilines <1989PHA294, 1989EJC259, 1987LA481> 1,2-oxathiin 2,2-dioxide derivatives 104 condensed to give the corresponding sultams 105 but 1,2-oxathiane 2,2-oxides 16 were cleaved by aniline or benzoylhydrazine derivatives to provide the corresponding sulfonic acids 106 (Scheme 25) <1993AFF256>. 

Similarly, using either sulfuric acid, the SOs/dioxane complex, or a solution of SO3 in chloroform/dioxane, 4,6-diphenyl-l,2-oxathiin 2,2-dioxide was obtained from phenyl acetylene <1999RJ0415>, 3,6-disubstituted-l,2-oxathiane 2,2-dioxides were obtained from allylphenol <2002RJ01210>, and 3,4-dihydro-6-phenyl-l,2-oxathiin-4-one 2,2-oxide was obtained from Ph-CO-CH2-COMe <1991CIL253>. 

Oxathiane 2-oxides aie fonned by the oxidative ring expansion of 2-alkylthio-2-benzylthiolane 1-oxides brought about by [bis(trifluoroacetoxy)iodo]benzene. That the reaction is only successful with the (lR )-diastereoisomeis is attributed to chelation between the nucleophilic S and O atoms and the hypervalent iodine <99EJ0943>. A diazo-mediated thiolane ring expansion is the key step in a synthesis of the acenaphtho-[U-b][l,4]oxathiine system <99JCS(P2)755>. 

A series of 4,6-disubstituted-l,3-dihydrothieno[3,4- ]thiophene-2,2-dioxides (sulfolenes) 477-480 was obtained <2002JOC9267> from 5,7-disubstituted l,4-dihydrothieno[3,4-7l[2,3]oxathiin-3-oxides (thienosultines) 476a-d by heating in benzene in sealed tube (Equation 15). 

The pyridazine dioxide derivative (108) was made by intramolecular nitroso compound dimerization as shown (Scheme 23). 1,2-Oxathiin 2,2-dioxides are obtained by the addition of sulfuric acid to a,(3-unsaturated ketones, e.g. (109) — (110) (66HC(21-2)774). 1,2-Dithiins are synthesized from conjugated diynes using benzyl thiol reductive debenzylation of intermediate (111) by sodium in liquid ammonia at - 70°C gives, after aerial oxidation, the 1,2-dithiin (112) (67AG(E)698). 

Desulfurization reactions in the 1,2-series are encountered among derivatives of both oxathiins and dithiins. 1,2-Oxathiin 2,2-dioxides extrude sulfur dioxide at elevated temperature over zinc oxide, iron or copper oxide to give the corresponding furan (66HC(21 -2)789) [cf. Section 2.26.3.1.2). Copper is a good catalyst for the extrusion of sulfur and sulfur dioxide from dibenzo[c,e3[l,2]dithiin (40) and its dioxide respectively to give dibenzothiophene (66HC(21-2)968). 

Dibenzo[c,e][ 1,2]oxathiin 6-oxide MS, 3, 957 (81JOC2373) Dibenzo[i/]phosphonin, 7-phenyl- H NMR, 7, 713 (80JA4838) Dibenzo[d/]phosphonin 7-oxide, 7-phenyl- H NMR, 7, 713 (80JA4838) Dibenzo[d/]phosphoninium, 7-methyl-7-phenyl- H NMR, 7, 713 (80JA4838)... 

For fiirther reactions of this type see <95CC2025>. The synthesis of l,4-dihydrofurano[3,4-d]-3,2-oxathiine-2-oxides, precursors for nonclassical heteroaromatic o-quinodimethanes, and their application in the Diels-Alder reaction were reported <95CC2537>. The intramolecular Diels-Alder reaction with furans (e. g., 47) offers a rapid access to highly functionalized isoquinolines <95 JCS(P 1)2393>. 

The first Diels-Alder [4+2]-cydoaddition functionalization of CNTs has been reported recently [171]. Ester-functionalized SWCNTs were reacted with o-quinodi-methane, generated in situ from benzo-l,2-oxathiin-2-oxide under microwave irradiation (Scheme 1.23). This technique opened up a new access to a novel family... 

An amount of 1.20 mg (0.9 mmol) of pentyl carboxylate-functionalized SWCNTs (Scheme 1.23) was mixed with 150 mg (0.9 mmol) of 4,5-benzo-l,2-oxathiin-2-oxide in 40 mL of ODCB and the mixture was irradiated in a focused microwave reactor at 150 W for 45 min. The ODCB was removed by vacuum distillation and the residue was purified by washing several times with pentane and diethyl ether to obtain benzobutenylene-functionalized SWCNT as a dark-brown solid [171]. 

A cyanosulfine [242] and an oxosulfine [162] were trapped with 2,3-dimethyl-1,3-butadiene (Table 6, entries 2 and 3). Capozzi and his group have extended their phthalimido-sulfenyl chemistry to the synthesis of a-oxosulfines, and have observed a dichotomic behaviour towards cycloaddition. With 1,3-dienes, these sulfines act [243, 244] as dienophiles through their C=S bond (Table 6, entry 4) to afford dihydro-2H-thiapyran S-oxides. With alkenes (Table 7), such as 2,3-dimethyl-2-butene (entry 1) or vinyl-ethers (entry 2), they behave as dienes to give dihydro-1,4-oxathiin S-oxides [243-245]. 

The /ra -6-fluoro-3,6-dihydro-1,2-oxathiin 2-oxide 126 prefers a conformation in which the ring oxygen lies almost in the plane of the four carbon centers and the S=0 bond resides in a pseudoequatorial orientation. The fluorine substituent adopts a stable pseudoaxial orientation. Quantum-chemical calculations suggest a stabilizing anomeric effect which was interpreted in terms of an n0 a C-F hyperconjugative interaction <2002CEJ1336, CHEC-III(8.10.3)688>. 

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