The cobalt-mediated [2+2+2]cycloaddition of thiophenes and benzofurans to alkynes
The cobalt-mediated [2+2+2]cycloaddition of thiophenes and benzofurans to alkynes was investigated. The cocyclization of 2-propynyloxymethylthiophenes provided two types of cyclohexadiene complexes. It was found that one of these complexes could be converted to the other by a thermal rearrangement. This novel transformation was investigated by deuterium-labelling and kinetic studies, and a mechanism was proposed. The complexes could be oxidatively demetallated to provide the liberated organic framework. Further reorganization of these dienes were observed during the decomplexation process and in the presence of CpCo(C[sub 2]H[sub 4])[sub 2]. In this manner several new heterocyclic ring systems could be constructed from 2-substituted thiophenes. Following the success of the thiophene cyclizations, the cocyclization of the benzofuran nucleus was examined. Reagents and conditions were developed that provide an efficient synthesis of alkynols from carboxylic acids; other functional group interconversions of the alkynols were briefly studied. The synthesis and cyclization of 1-[7-methoxy-4-benzofuranyl]-3-butyn-2-ol produced a cobalt complex containing the A,B,C, and D rings of the morphine skeleton. A synthetic advantage of this methodology would be the ease of substitution at pharmaco-logically relevant C-6 and C-7 positions of the morphine framework. Synthetic routes using a cobalt cyclization strategy were proposed.
- Research Organization:
- California Univ., Berkeley, CA (United States)
- OSTI ID:
- 5602572
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
ALKALOIDS
ALKYNES
ANALGESICS
BENZOFURANS
CENTRAL NERVOUS SYSTEM DEPRESSANTS
CHEMICAL PREPARATION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COBALT COMPLEXES
COMPLEXES
CYCLIZATION
DEMETALLIZATION
DEUTERIUM
DEUTERIUM COMPOUNDS
DRUGS
FURANS
HETEROCYCLIC COMPOUNDS
HYDROCARBONS
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
ISOTOPES
KINETICS
LABELLED COMPOUNDS
LIGHT NUCLEI
MORPHINE
NARCOTICS
NUCLEI
ODD-ODD NUCLEI
OPIUM
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
ORGANOMETALLIC COMPOUNDS
POLYCYCLIC SULFUR HETEROCYCLES
REACTION KINETICS
SEPARATION PROCESSES
STABLE ISOTOPES
SYNTHESIS
TRANSITION ELEMENT COMPLEXES