Reviews and Accounts ARKIVOC 2013 (i) 396-417
1. Introduction The formation of carbon-carbon double bond is of fundamental importance in organic synthesis because it allows the introduction of a wide variety of functional groups. As a result, many reactions and reagents have been developed for carbon-carbon double bond formation. Several reagents were utilized by us to obtain alkenes from the carbonyl compounds. The present account is largely a survey of the reagents utilized between 1990-2012 at the Department of Chemistry, IVIC, Caracas and University of Zulia, Maracaibo, Venezuela, for the synthesis of alkenes from carbonyl compounds and their utility in the synthesis of terpenoid compounds.
2. Reagents for the Conversion of Carbonyl into Alkene 2.1. Lithium bromide (LiBr), lithium carbonate (Li2CO3) and dimethylformamide (DMF) The combination of LiBr and Li2CO3 in DMF is a powerful reagent for detosylation to yield alkene. Therefore for the conversion of the ketone into an alkene, a carbonyl group is converted into a tosyl group by reduction and detosylation. The combination of these reagents has been frequently used in our laboratory. Some examples are cited below: Ketoester1 2, prepared from the octalin 1, on reduction with sodium borohydride in methanol yielded a mixture of alcohols whose tosyl derivative on heating with LiBr, Li2CO3 and DMF afforded the alkene1 3 which was converted into the methylene decalone2 4 in four steps (bromohydrin reaction, oxidation, dehydrohalogenation, and oxidative decarboxylation).
Me Me Me Me Me COOMe O Me Me COOMe Me O H (i), (ii) (iii) (iv), (v), (vi) (vii) H H 4
1
3
2
Me Me
(x) (viii), (xi)
Me
Me H
OH
H
Me
Me
56
Reagents: (i) NaBH4, MeOH; (ii) TsCl/Py; (iii) Li2CO3, LiBr, DMF; (iv) NBS, DMSO; (v) CrO3, Me2CO3, (vi) collidine, (vii) Pb(OAc)4, C6H6, Py; (viii) CO(COOMe)2, DME, NaH; (ix) MeLi, Et2O (2M); (x) SOCl2, Py
Scheme 1
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