Chemistry of 1-Carbena-5-hexyne and Related Intermediates

Article abstract of DOI:10.1021/jo00299a032

Pyrolysis of the lithium salt of the tosylhydrazone of 4,4-dimethyl-6-heptyn-2-one (6b) as the dry salt over a temperature range of 150 to 200 deg C formed 4,4-dimethyl-1-hepten-6-yne (8), cis-4,4-dimethyl-5-hepten-1-yne (9), and trans-4,4-dimethyl-5-hepten-1-yne (10) with an average acyclic enyne composition of 11.1:4.9:84.0.The fourth product component, 1,5,5-trimethyl-1,3-cyclohexadiene (11a), was formed in 22-28percent relative to the acyclic enyne fraction.In order to test for a carbene to carbene equilibration, the lithium and sodium salts of 3,5,5-trimethyl-2-cyclohexenone tosylhydrazone were pyrolyzed.The lithium (sodium) salt formed 95.2percent (96.7percent) 11 and 4.8percent (3.3percent) 5,5-dimethyl-1-methylene-2-cyclohexene (19).Pyrolysis of the sodium salt of 4,4-dimethyl-6-heptyn-2-one (6c) generated an increased amount of cyclic product exhibiting a product composition of 72.0percent 11a, 8.7percent 8, 2.3percent 9, and 17.0percent 10, whereas the pyrolysis of 6c in the presence of 3.0 equiv of LiBr produced a product composition poorer in cyclic product (34.6percent 11a, 13.2percent 8, 5.2percent 9, and 47.2percent 10).Thermolysis of the lithium (sodium) salt of the tosylhydrazone of 2-heptanon-6-yne generates products with a reaction composition of 4.8percent (47.8percent) 1-methyl-1,3-cyclohexadiene (11b), 8.1percent (5.9percent) 1-hepten-6-yne (21), 29.9percent (11.4percent) cis-5-hepten-1-yne (22), and 57.3percent (35.1percent) trans-5-hepten-1-yne (23).In order to characterize the alkynylcarbenes formed in these decompositions, the related saturated systems were investigated by pyrolysis of the lithium and sodium salts of the tosylhydrazones of 2-heptanone and 4,4-dimethyl-2-heptanone.The mechanistic pathways for the decomposition of 2-diazo-4,4-dimethyl-1-heptyne are described in terms of (a) a pyrazole route and (b) a carbene to carbene rearrangement.