Grignard reagents thienyl, reactions

Cyanothiophene is most conveniently derived from the aldehyde oxime by dehydration (equation 23), but has also been obtained by reaction of the 2-thienyl Grignard reagent or 2-thienyllithium with cyanogen chloride. Activated halogens are readily displaced by cyanide ion (equation 24 Section 3.14.2.7). 

Thiophenethiols are prepared by reduction of the sulfonyl chlorides or, more conveniently, by the reaction of Grignard reagents or thienyllithium compounds with sulfur. They have also been obtained by cleavage or thienyl alkyl sulfides with sodium in liquid ammonia. 3-Thiophenethiol is a by-product in the commercial thiophene synthesis. Thiophenethiols have recently also been prepared by a synthesis involving Friedel-Crafts reaction of 2,4-dinitrobenzenesulfenyl chloride with thiophenes, followed by basic cleavage of the resulting sulfide. ... 

The reaction of -thionyldiimidazole with aryl Grignard reagents is a standard procedure for the synthesis of symmetrical sulfoxides. when applied to thienyllithium, a high yield (84%) of the ligand coupling product (193) was serendipitously obtained instead of the expected di(2-thienyl) sulfoxide. 

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. 

The use of thienyl Grignard reagents, and more recently lithiated thiophenes, has been extensive and can be illustrated by citing formation of oxythiophenes, either by reaction of the former with f-butyl perbenzoate or the latter directly with bis(trimethylsilyl) peroxide or via the boronic acid, the synthesis of thiophene carboxylic acids by reaction of the organometallic with carbon dioxide, the synthesis of ketones, by reaction with a nitrile, or alcohols by reaction with aldehydes, by the reaction of 2-lithiothiophene with A -tosylaziridine, and by syntheses of thieno[3,2- ]thiophene and of dithieno[3,2- 2, 3 - /]thiophene. Some of these are illustrated below. 

Reactions of Thiophen Aldehydes and Ketones.—The synthesis of bis-(4-methylpent-3-enyl)thiophens was achieved by applying the Wittig reaction to (106). A convenient method for the synthesis of (2-thienyl)ethylene oxide from thiophen-2-aldehyde and a sulphur ylide has been worked out. From 2-thenil and diethyl ketone, (107) was prepared, and its Diels-Alder reactions have been studied. The reaction of (108) with different Grignard reagents has been... 

Reaction of 4-chloro-l-(2-thienyl)-l-butanone (20) with the Grignard reagent (21) provided the 2,2-disubstituted tetrahydrofuran (22) in good yield. The tet-rahydrofuran ring could be opened with concomitant dehydration to provide an... 

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