Diazo-thioketone coupling

Various substituted naphtho[2,l-f>]thiopyran-l -ylidene-9H-thioxanthene derivatives 23 have been synthesised using diazo-thioketone coupling as the key step. The compounds function as light-driven molecular motors and studies of the photochemical and thermal isomerisation processes indicate a four-step unidirectional 360° rotation about the double bond of the upper half of the molecule with respect to the lower half <02JA5037>. 

The Barton-Kellogg reaction is a coupling reaction between a diazo compound and a thioketone to give an episulfide. Desulfurization of the episulfide to alkene can be accomplished by phosphine or by copper powder. This reaction has been pioneered by Hermann Staudinger and therefore the reaction also goes by the name Staudinger-type diazo-thioketone coupling. 

The main advantage of this reaction over the McMurry reaction (see section on McMurry alkenation ) is the notion that the reaction can take place with two different ketones. In this regard the diazo-thioketone coupling is a cross-coupling rather than a homocoupling. 

Figure 1.10 Scheme of the Barton-Kellogg reaction for modified diazo-thioketone coupling for the synthesis of overcrowded alkenes. (Reproduced with permission from Ref [59].)... 

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