2.3- Dihydro-1,4-oxathiins

Derivatives of 2,3-dihydro-1,4-oxathiin and 1,4-benzoxathiins have been patented as agrochemicals. An important development in fungicidal research has been the discovery of so-called systemic fungicides. Unlike surface fungicides which may require repeated... 

Addition of thiols to alkenes/alkynes. Formation of 2,3-dihydro-1,4-oxathiins by cycloaddition and alkenyl suffides by simple addition is catalyzed by Mn(0Ac)3-2H20. 

Derivatives of 2,3-dihydro-1,4-oxathiin have been patented as agrochemicals. Thus, 5,6-dihydro-... 

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,... 

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>. 

Further, a 1,2-oxathiane 2,2-dioxide derivative was obtained as a by-product (15-25%) in the enantioselective synthesis of Oasomycin A <2007AG545> all efforts to suppress this side reaction were not successful, and the reaction products of the hexafluorobutadiene sulfotrioxidation (among the main products a 4,5-dihydro-l,2-oxathiin 2,2-dioxide derivative) were identified by F NMR spectroscopy <2007RJA424>. 

Most partially saturated ring systems, 2,3-dihydro-l,4-dioxin 10 (sometimes named as 1,4-dioxene), 2,3-dihydro-1,4-dithiin 11, 2,3-dihydro-l,4-oxathiin 12, 2,3-dihydro-l,4-benzodioxin or 1,4-benzodioxane 13, 2,3-dihydro-l,4-benzodithiin 14, and 2,3-dihydro-l,4-benzoxathiin 15 are well investigated. Ring numbering for compounds 10-12 is followed as shown, independently of the presence of substituents. 

Dihydro-1,4-oxathiins (336 Z = 0) and 5,6-dihydro-1,4-dithiins (336 Z = S) are easily obtained from 1,3-oxathiolanes (335 Z = 0) and 1,3-dithiolanes (335 Z=S), respectively, by treatment with bromine (9IS223), A-bromosuccinimide (94T7265), chlorine (87JOC5374, 91S223), or sulfuryl chloride (88JCR(M)1401>. 

The monobenzo-fused derivatives of 1,4-dioxin, 1,4-oxathiin and 1,4-dithiin, (345), (346) and (347), can all be prepared by base-catalyzed reaction between the appropriate 1,2-disubstituted benzene and an a-haloketal via an intermediate 2-alkoxy-2,3-dihydro derivative (348). The pyrolysis of the acetoxy derivative (349) at 450°C gives (345 80%) (67ZC152). 2-Hydroxy-2-phenyl-l,4-benzodioxane, from catechol and phenacyl bromide, is dehydrated to (345) by thionyl chloride in pyridine. 

The double bonds in 2,3-dihydro-l,4-dioxin, 2,3-dihydro-l,4-oxathiin and 2,3-dihydro-1,4-dithiin undergo standard electrophilic addition reactions. Under acid catalysis, methanol adds to 2,3-dihydro-l,4-oxathiin to give 2-methoxy-1,4-oxathiane (66HC(21-2)842). Various examples are available of reactions of the double bonds with carbenoids to give bicyclo[4.1.0]diheteroheptanes (77LA910,78ZC15), and with alkenes in [2 + 2] cycloadditions (78CB3624). 

Various dihydro-1,4-oxathiins and dihydro-1,4-dithiins are reported to be useful in areas other than agriculture. Thus, 2,3-dihydro-l,4-dithiin-5,6-dicarboximides display a wide spectrum of biological activity (77SST(4)332) while derivatives of the basic structure (243) have been patented as tranquilizers, anticonvulsants and hypnotics (76GEP2550163). Sedative, myorelaxant and cataleptic properties are associated with certain 2,1-benzoxathiane 2,2-dioxides (75BRP1383459). 

Optically pure 1,3-oxathiins have been used as chiral auxiliaries for the synthesis of (E)-monoaryl epoxides (95JOC3494) and (5-substituted ketones (95SL501), whilst the desulfurisation of some dihydro-1,4-oxathiins affords E-alkyl vinyl ethers (95SL1274). 

In the oxygenation of 5,6-dihydro- 1,4-oxathiin 116, despite the presence of allylic hydrogens and the sulfide moiety, the sole reaction product is the dicarbonyl compound 118 (isolated yield 90%) [126a] deriving from the corresponding dioxetane 117, which has been spectroscopically... 

Intramolecular nucleophilic attacks of nitrogen [106a] and sulfur [126] at 0-0 bond have been recently proposed to explain the formation of unexpected products in the oxygenation of 2(o-aminophenyl)-4,5-dihydro-furans 148 (Sch. 81) and 5,6-dihydro-l,4-oxathiins 149 (Sch. 82). 

In the latter cases, the stereoselective formation of keto sulfoxides 153 and 154 has been observed instead of the expected dicarbonyl compounds 151 (as found for 3-methyl-2-phenyl-5,6-dihydro-1,4-oxathiin (116), Sch. 67), only in the presence of an electron withdrawing group at the double... 

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>. 

Oxathiin 2,2-dioxides (sultones) (e.g., 150) are obtained by the addition of sulfur trioxide to dienes or by ringclosing metathesis (RCM) of sulfonates using the second-generation Grubbs ruthenium catalyst (Scheme 75) . The same catalyst was also successfully employed in the RCM of diallyl disulfide 151 which led quantitatively to 3,6-dihydro-l,2-dithiin 152 (Scheme 76) <20020L1767>. 

Dioxins, 1,4-oxathiins, and 1,4-dithiins are commonly prepared by elimination reactions from saturated analogues (see Section 4.3.4.1.4). A convenient synthesis of 2,3-dihydro-1,4-dioxins (e.g., 442) starts from propargyl chloride and 1,2-ethanediol (Scheme 206) . Another approach to substituted 2,3-dihydro-... 

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