- Chemistry of 1-Carbena-5-hexyne and Related Intermediates
-
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.
- Freeman, Peter K.,Danino Jose C.,Stevenson, Brian K.,Clapp, Gary E.
-
p. 3867 - 3875
(2007/10/02)
-
- Silanes in Organic Synthesis. 8. Preparation of Vinylsilanes from Ketones and Their Regiospecific Cyclopentenone Annulation
-
A general method is described for the formation of vinylsilanes from ketones.Thus, conversion to the benzene- or p-toluenesulfonylhydrazone and sequential treatment with n-butyllithium and chlorotrimethylsilane in anhydrous tetramethylethylenediamine proceeds regiospecifically to afford the less substituted vinylsilane (in unsymmetrical cases).Friedel-Crafts acylation with acryloyl chlorides and aluminium chloride and subsequent Nazarov cyclization with Lewis acid catalysis results in cyclopentenone annulation.Numerous examples that reveal the scope of this processare described.Due to accompanying polymerization, annulation with acryloyl chloride itself is least efficient.This complication can, however, be averted through use of β-chloropropionyl chloride and dehydrochlorination with 1,5-diazabicycloundec-5-ene prior to ring closure.
- Paquette, Leo A.,Fristad, William E.,Dime, David S.,Bailey, Thomas R.
-
p. 3017 - 3028
(2007/10/02)
-