Benzo thiepin

Only limited IR spectroscopic data for (benzo)thiepins have been reported. The C —C double bond stretching frequency in 2,7-di-rm-butyl-4,5-dimethylthiepin is observed at 1620 cm-1 with weak intensity.13 Characteristic strong intensities are found for the S —O vibrations in sulfoxide (e.g., 1040 cm-1 for 5-methoxy-4-phenyl-l-benzothiepin-3(2//)-one 1-oxide14) and sulfone (e.g., 1120 and 1300 cm-1 for thiepin 1,1-dioxide15) derivatives. 

Besides a parent ion, the mass spectra of benzo- and dibenzothiepins show the corresponding naphthalene or phenanthrene radical cations as the base peak.2-16 The mass spectra of 1-benzo-thiepin 1-oxides and 1,1-dioxides show the same naphthalene radical cation, formed by loss of sulfur monoxide or sulfur dioxide, respectively.14 In contrast, in the mass spectrum of 2,7-di-terf-butylthiepin peaks resulting from the loss of sulfur are not found.17... 

Tabic 3. 13CNMR Spectra of (Benzo)Thiepins in CDC13 (Chemical Shifts in ppm)... 

Table 4. Bond Lengths and Dihedral Angles of (Benzo)Thiepins...

Benzo)Thiepin Bond Length (A) Dihedral Angle Ref... 

Due to their thermal instability, this method cannot be applied to the preparation of benzo-thiepins. Although the ft-oxo sulfoxide moiety in precursors such as 5-methoxy-4-phenyl-l-benzothiepin-3(2/7)-one 1-oxide makes them candidates for a Pummerer reaction, treatment with acetic anhydride and triethylamine at - 30 C results in preferential enol acetylation to afford the corresponding 1-benzothiepin 1-oxide.14... 

Starting from l.l-dichloro-7b-ethoxy-2-methyl-1,1 a,2,7-tetrahydrobenzo[/)]cyclopropa[prepared from the corresponding benzothiopyran by addition of dichlorocarbene, the three 1-benzothiepins 6a-c are formed upon treatment with strong bases, i.e. sodium methoxide or ethoxide in dimethyl sulfoxide.73 The optimal yield of each 1-benzo-thiepin compound depends on the molar equivalents of base, as follows from different ring-opening mechanisms. 

Benzothiepins synthesized by a double Knoevenagel condensation (see Section 2.1.1.2.) contain free carboxylic acid groups if the reaction product is isolated under acidic conditions. Rcesterification can be performed by two methods via formation of the acid chloride and subsequent alcoholysis, or by reaction with diazomethane, e.g. the conversion of 3-benzo-thiepin-2,4-diearboxylic acid (5, R = C02H) with thionyl chloride and methanol gives the dimethyl ester 5 (R = C02Me) in 47% yield, while the diazomethane pathway provides 60% of the dimethyl ester.65 Use of excess diazomethane leads to cycloadducts (see Section 2.2.4.). 

The greater lability of 1-benzothiepin 1-oxides, compared to the parent compounds, may lead to differences in chemical behavior. Thus, treatment of the tricarbonyliron complex of 1-benzo-thiepin 1-oxide (8, X = SO) with ammonium cerium(IV) nitrate in acetone at — 30 °C leads, with the loss of sulfur monoxide, to naphthalene. In contrast, the iron ligand can be removed selectively from the corresponding 1-benzothiepin by ammonium cerium(IV) nitrate.23 92 For the synthesis of 1-benzothiepin 1-oxide, see Section 2.1.4.1,... 

The first attempted synthesis of a benzo[ ]thiepin derivative was the solvolysis of 7,7-dichloro-3,4-benzo-2-thiabicyclo[4.1,0]heptene (19)20). Unfortunately, the reaction of 19 in hot quinoline led to 2-chloronaphthalene which suggested the reaction mechanism as shown below. In the case of the reaction of l,l-dichloro-7b-ethoxy-... 

Firstly, the electronic effect of the substituents would be a dominant factor in the determination of the thermal stability of the thiepins. Thermal stability was found to decrease sharply with decreasing substitution. For example, the tri-substituted benzo-[6]thiepin (16 d) extrudes sulfur only when heated while the non-substituted benzo[ >]-thiepin (4) is readily converted into naphthalene and sulfur at 40 °C with a half-life of 80 min 41 >. 

A wide variety of photoreactions have been reported in sulphur-containing compounds, with particular attention being paid to the photochemistry of thiones. Electrocyclic ring closure to the eyelobutabenzo[b]thiophenes (131) is the principal reaction observed on irradiation of the mono-substituted 1-benzo-thiepines (132). Photorearrangement of the 2-methyl-1,5-benzo-thiazepines (133) takes a different course and affords the isomeric... 

Dihydro-1-benzothiepin is converted into 2,3-dihydro-l-benzo-thiepin 1-oxide with sulfuryl chloride in 79% yield or with sodium periodate in 77% yield (equation 562) [5%]. 

Compounds (210) are prepared from 2H-l-benzothiopyran (209) by metalation with -butyl-lithium and subsequent reaction with dichloromethane (and alkylation of (210) via the anion). Treatment of (210) with dicarbonyl-2,4-pentanedionatorhodium(I) gives the isomerized 1-benzo-thiepines (2) and (82a,b). The last step is mild enough ( 0°C) to enable isolation of even the labile 1-benzothiepine (2) (Scheme 36) <74AG161,75TL2697,76BCJ825>. 

Thiepine oxides are thermally less stable than the corresponding thiepines and thiepine dioxides 2,7-di-(-butylthiepine 1-oxide (25) was detected only at low temperatures <94JCS(P1)2631>. 1-Benzo-thiepine 1-oxides stabilized by substituents were prepared and isolated by oxidation of the corresponding thiepines <75AG(E)812> (see Section 9.03.4.3). However, synthesis of labile 1-benzothiepine 1-oxide (26) failed under either oxidative or traditional reaction conditions. Alternatively, (26) was derived from 1 -benzothiepine 1 -oxide (30) (tricarbonyl)iron at — 50 °C by oxidative removal of Fe(CO)3 <88AG(E)1717>. 

The ring-opening of cyclobutene to butadiene has been employed in the first synthesis of monocyclic thiepins by thermolysis of the thiophen-ADE adducts (593) and has been applied in a similar fashion to syntheses of benzoxepins and benzo-thiepins. ... 

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