Dibenzo thiepin-5-ones

Dibenzo[/),/]thiepin-10(l 1H)-one (1) is an important synthon for the transformation of thiepins into other heterocycles. Oxidation with selenium(IV) oxide gives dibenzo[7>,/]thiepin-10,l 1-dionc (2), in 45% yield,38 which can be condensed with a series of benzaldchydes in the presence of ammonium acetate to provide the substituted 2-aryldibenzo[2,3 6,7]thiepino[4,5-t/]imidazoles 3, known to have anti-inflammatory properties.38... 

One equivalent of bromine is added smoothly to the C10-C11 -double bond, which has nearly olefinic character, of dibenzo[/>,/]thiepin in 88% yield (see Section 2.I.4.3.).3... 

According to the Hantzsch-Widman system, the seven-membered unsaturated hcterocyclc with one sulfur atom is named thiepin (1). The three different benzothiepins are assigned by the position of sulfur 1-benzothiepin (2), 2-benzothiepin (3) and 3-benzothiepin (4). Of the four possible dibenzothiepins only dibenzo[6,r/]thiepin (5) and dibenzo[A,/]thiepin (6) are of importance for synthesis, while the other two isomers, which contain unfavorable o-quinoid structures, exist mainly as the stable dihydro compounds, i.c. 5,7-dihydrodibenzo[c,t ]thiepin (7) and 6,1 l-dihydrodibenzo[6,c ]thiepin (8). Benzannulation over all double bonds results in tri-benzo[6,(7,/]thiepin (9). 

One equivalent of bromine was added to dibenzo[7 /]thiepin (1) and then the isolated dibromide was treated with 1-methylpiperazine in benzene at room temperature. Upon crystallization, 10-bromodibenzo[/),/]thiepin (2) was obtained in 51 % yield.3... 

Chlorodibenzo[, /]thiepin (4) can be obtained in 62% yield from dibenzo[6,/]thiepin-10(ll//)-one (3) in the presence of phosphoryl chloride and zinc(II) chloride, but a one-step ring-closure synthesis (sec Section 2.1.1.1.) yields 4 in 86% yield.3... 

Dibenzofuro[4,5-c]tropone (8H-dibenzo[a,e]furo[3,4-c]cyclohepten-8-one 368, X = CO) and the corresponding thiepin-5,5-dioxide (8//-dibenzo-[6,/]furo[3,4-retro Diels-Alder route. In refluxing benzene, the intermediate (367, X = CO) can be isolated. Further routes to 368 (X = CO) by retro Diels-Alder reaction exist. The 1-methyl derivative of 368 (X = CO) has been trapped as a maleic anhydride adduct. ... 

Reaction of 117/-dibenzo[7/]thiepin-10-ones 135a and 135b with chloroacetone in the presence of base in dimethyl sulfoxide (DMSO) resulted in formation of O-alkylation products 136a and 136b in 23% and 8% yields, respectively (Equation 18) <2006JHC749>. On the other hand, oxepine analogs preferentially gave G-alkylation products. 

Dibenzo[fcj/ oxepin-10(l lfi)-one and dibenzo[6 thiepin-10(llH)-one as useful synthons in the synthesis of various dibenzo[e,/j]azulenes 12JHC243. 

The relative ease of the cyclization step from A to C may also be linked to the nucleophilic or coordinative ability of the heteroatom bound to the metal. The reaction of 7 with diphenylacetylene (Ph2C2) leads to the seven-membered derivatives 68 and 69 after prior isolation of the monoinsertion product 24, treatment with a silver salt, followed by the usual thermolytic conditions. This is another rare example of an intramolecular formation of a C-S bond within the coordination sphere of a transition metal and a novel, albeit limited to one alkyne, route to the rare family of dibenzo[bd] thiepins. With the closely related 8, which differs from 7 only by the tertiary amine unit in the metallacyclic framework instead of a thioether function, a carbocyclic product 71 is obtained (see under carbocycle reactions, next section). The formation of the seven-membered S-heterocycles is attributed to the good coordinative ability of the thioether group in 7. The S-atom remains close to the vinylic carbon function before the cyclization. With the poorly coordinating, readily displaced amine function in 8, the N-atom is detached from the metal and ultimately affords a spirocyclic product (see Scheme 18). 

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