5- Bromobenzo thiophene dioxide

The normal reactions of benzo[6]thiophene 1,1-dioxides have been reviewed (70AHC(11)177). Electrophilic substitution (nitration, bromination) takes place at position 6. 3-Halo derivatives undergo normal nucleophilic displacement reactions, but 2-bromobenzo[6]thiophene dioxide gives the 3-ethoxy derivative in ethanolic NaOH. The reaction of 3-methoxy derivatives with secondary amines can give rise either to enamines... 

Bromobenzo [ ] thiophene 1,1-dioxide 117 and 3-bromo-2-phenylbenzo-[b]thiophene 1,1-dioxide 119 reacted with ammonia and primary and secondary amines to give the corresponding 3-aminobenzothiophene dioxides, 118 and 120, in good yields (Scheme 68) [17, 192-194]. 2-Benzoyl-3-chloro-benzo[ ]thiophene 1,1-dioxide 121 also reacted with a series of nitrogen nucleophiles to give substitution products 122 in good yields (Scheme 69) [195]. 

The addition of hydrogen bromide and sulfur dioxide to phenylpropiolic acid (210) in diethyl ether at -50 °C is reported to give 3-bromobenzo[6]thiophene-2-carboxylic acid (211) (75ZOR1776). If hydrogen bromide and sulfur dioxide can react under these conditions to give thionyl bromide, the reaction is similar to the reaction of thionyl chloride with unsaturated acids, reported in the previous section. 

V-Substituted 3-aminobenzo[6]thiophenes are readily obtained by heating thioindoxyl with the appropriate primary or secondary aromatic amine,539 541,553,554 or primary aliphatic amine541 (Section VI, 1,2). 3-A7,jV-I)ialkylaminobemo[ ]thiophenes are best obtained by reaction of 3-bromobenzo[6]thiophene-1,1 -dioxide with a secondary aliphatic amine, followed by reduction of the product with lithium aluminum hydride (Section VI,P,2,/).541 3-Amino-2-nitrobenzo[6]-thiophene and its A-substituted derivatives are conveniently obtained... 

Benzo[ ]thiophene 1,1-dioxide 38 and its derivatives act as typical a, ft-unsaturated sulfones, and a variety of nucleophiles add to the carbon atom at the 3-position. Thus, amines and the conjugated bases of water, alcohols, thiophenol, and diethyl malonate all add to 38 to give the corresponding adducts 110 in excellent yields (Scheme 65) [189]. Even hydrogen bromide can add to 38. When 2-bromobenzo[b]thiophene 1,1-dioxide 111 was treated with piperidine and morpholine under appropriate conditions, excellent yields of adducts 112 were isolated without being accompanied by dehydrobromination (Scheme 66) [190]. 

Nucleophilic substitution in 2,3-dichlorobenzo[b] thiophene 1,1-dioxides takes place preferentially in the 3-position.352 2-Bromobenzo[i>]thiophene 1,1-dioxide is converted into the 3-bromo isomer by KNH2-NH3215 it is well established that a 2-bromine atom is replaced by a nucleophile with rearrangement to give the 3-substituted product.1 A 3-chloro substituent, activated by an adjacent ester or ketone function, is very readily replaced, and cyclization can often take place to form an additional heterocyclic... 

Scheme 72 Dimerization of 4-nitrobenzo[i)]thiophene 1,1-dioxide and 5-bromobenzo[6]thio-phene 1,1-dioxide [95]...

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