Of dithienylalkanes

Details of the various syntheses of dithienylalkanes and related compounds that involve condensations with aldehydes and ketones are compiled in Tables I and II (which refer to Eqs. 4 and 1 [X = Y = O], respectively.)... 

Almost all reports of acylation of dithienylalkanes have involved 2,2 -derivatives with free 5- or 5,5 -positions (Eq. 20) details are compiled in Table VI. The catalysts employed have been those commonly used with thiophenes, i.e., tin(IV) chloride for acid chlorides and anhydrides and polyphosphoric acid for carboxylic acids. Iodine has often been the catalyst for the reaction of dithienylalkanes with acetic anhydride perchloric acid has also been used.39 Bisacylation is often observed and can be made the major reaction by use of an excess of reagent. 

Ahmed and Meth-Cohn26,96 found the lithiation of 2,2 -dithienylmethane to be temperature dependent. Below — 10°C monolithiation and above + 5°C dilithiation were observed at intermediate temperatures mixtures were obtained. Once formed, the lithio derivatives of dithienylalkanes behave unexceptionally. A summary of results from 2,2 -dithienylmethanes is presented in Table VII (Eq. 21). 

Very little information is available on the mass spectroscopic behavior of dithienylalkanes, but it is clear that an important fragmentation of compounds of the type (2-C4H3S)2CHX is the loss of X, presumably to produce... 

Directed metalation of -deficient azaaromatics strategies of functionalization of pyridines, quinolines, and diazines, 52, 187 gem-Dithienylalkanes and their derivatives, 32, 83... 

Electropolymerization with formation of conducting polymers 86CJC76. gem-Dithienylalkanes, general review 82AHC(32)83. 

Catalytic synthesis of thiophene and alkylthiophenes 71KGS1299. Coordination compounds with thiophene derivatives as ligands 76MI1. Dithienylalkanes, synthesis of 82AHC(32)83. 

The main interest in t/ero-dithienylalkane derivatives in recent years has been in their use as synthetic intermediates, via reductive desulfurization, for a variety of aliphatic substances (notably carboxylic acids) and as sub-... 

The nomenclature for gem-dithienylalkanes is reasonably straightforward, the thiophene rings being described as substituents of the parent alkane. Compound 6 is thus 2,2-bis(2-thienyl)butane, and 7 is l-chloro-2,2-bis-(5-ethyl-2-thienyl)ethane. 

Dithienylalkanes occur in certain shale oils of high sulfur content. The compounds described4,5 are bis(5-methyl-2-thienyl)ethanes and -propanes, both with and without additional methyl groups in the thiophene rings 5,5 -dialkyl-2,2 -dithienylmethanes are also present. A patent6 refers to the use of l,l-bis(2-thienyl)ethane, 2,2-bis(2-thienyl)propane, and 2-hydroxy-phenylbis(2-thienyl)methane as antioxidants for mineral oils, but otherwise there seems to be no commercial use for simple dithienylalkanes. 

In the second class of synthesis two thiophene rings become joined through a carbon atom that is already a substituent of one of them by this means symmetrically and unsymmetrically substituted products in the 2,2, 2,3, and 3,3 series are available. Three main reaction types have been employed in this approach. In one of these a thiophene is alkylated with a thenyl halide (Eq. 3). Friedel-Crafts acylation of a thiophene by a thenoyl chloride or thenoic acid followed by reduction of the resulting dithienyl ketone provides a second route in this category. The last and most versatile synthesis in this class involves reaction of a thienyllithium (or Grignard reagent) with a thienylaldehyde or thienyl ketone reduction of the carbinol (see Eq. 2) then gives the dithienylalkane. 

A more detailed survey of these reactions will now be given the section concludes with an account of some other, less general reactions that have led to dithienylalkanes. 

In the presence of a suitable catalyst the dithienylalkane becomes the major product in these reactions with chloroalkyl ethers. The catalysts employed have included tin(IV) chloride,51 aluminum chloride,23 concentrated sulfuric acid,25 and zinc dust.52 53 It is suggested in the last case that the zinc and chloroalkyl ether react to produce the aldehyde and zinc chloride (Eq. 5a). However, it seems more likely that some zinc chloride would be produced in a coupling reaction (Eq. 5b) and would then catalyze the condensation of thiophene and the chloroalkyl ether in the usual way. With a sufficiently vigorous catalyst even deactivated... 

The thiophene rings in simple dithienylalkanes possess about the same level of reactivity as those in simple alkylthiophenes. Peter1 noted a violent reaction when 2,2 -dithienylmethane was treated with fuming nitric acid. 

The same considerations concerning delocalization of charge in dithienylalkane anions can be applied to the comparable cationic derivatives in... 

Substituents on dithienylalkanes behave normally. Certain reactions of readily accessible derivatives have been well studied others have received scarcely any attention. 

Interest in dithienylalkanes of potential pharmacological importance was aroused by the discovery that some 3-dialkylamino-l,l-bis(2-thienyl)but-l-enes possess analgesic activity.116 Compounds 91, termed thiambutenes, are prepared by dehydration of carbinols of general formula 92. Considerable variations in the substituents have been made in the search for greater activity and for a reduction in undesirable side effects often, these variants have both analgesic and antitussive properties. Substances with obvious structural similarities to 91 and 92, namely, the thiophene analog of methadone (93) and of isomethadone, have also been prepared.63,107... 

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