Acyclic decomposition routes

Ketocarbenes of type (21) obtained from acyclic and medium to large ring alicyclic a-diazo ketones (20) are prone to react by way of an intramolecular [1,2] H-shift, especially under catalytic conditions, to afford a, 3-unsaturated ketones (22). °4 -60 Pranzen has shown that the Wolff rearrangement of diazo ketones (20) is favored if temperatures in excess of 100 °C are used in the photochemical or Ag20-pro-moted decompositions. Related [1,2] methyl shifts can also occur, and this pathway is the principal decomposition route of 4-diazo-2,2,5,5-tetramethyl-3-hexanone. ... 

Scheme 16.3 Decomposition routes of acyclic carbene ligands.

Acyclic azo compounds are obtained by usual routes only as frans-isomers. Photochemical isomerisation provides an easy and effective way to the cis-isomers. The cfs-azo compounds are however thermally quite labile and decompose with elimination of nitrogen 41>, some of them even at —120 °C 5>. Activation energies for the thermal decomposition of cfs-azo-alkanes are of the order of 20... 

A synthesis of acyclic 1,5-dienes is exemplified by the route shown in Scheme 18. In all cases cleavage of the more substituted of the two equivalently orientated jS,y-cyclohexane ring bonds occurred in the boronate decomposition (279). A further route to these synthetically valuable 1,5-dienes is... 

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