NAZAROV Cyclopentenone Synthesis

NAZAROV Cyclopentenone synthesis Acid catalyzed cyclaation of dienones to cyclopentenones... 

NAZAROV Cyclopentenone Synthesis Acid catalyzed of dienones to cyclopentenones (see 1st edition). 

Organic Syntheses Based on Name Reactions NAZAROV Cyclopentenone Synthesis... 

NAZAROV Cyciopentenone synthesis Acid catalyzed cyclization of dtenones to cyclopentenones... 

Cyclopentenone Synthesis. When activated with Lewis acid catalysts or silver ion, 1-phenylthio-l-trimethylsilylethylene reacts with a,/3-unsaturated acid chlorides at a low temperature in CH2Cl2. The cation intermediates undergo a silicon-directed Nazarov cyclization to give 3-phenylthio-substituted cyclopentenone derivatives (eq 3). The phenylthio moiety at the /3-position of cyclopentenones can be effectively utilized for the introduction of an alkyl substituent by addition/elimination. 

Cyclopentenone annelation (cf. 10,444). The reagent undergoes a Nazarov-type cyclization with an a,/S-unsaturated acid chloride to give an annelated 3-phenylthio-cyclopentenone. This reaction was used to prepare the bicyclic cyclopentenone 3, a useful intermediate in synthesis of cyclopentenoid natural products, such as hirsutene (4).3... 

The Nazarov Cyclization allows the synthesis of cyclopentenones from divinyl ketones. 

A synthesis of cyclopentenones somewhat related to those shown earlier was found from conjugated 1,3-enynes (equation 19) Cyclopentenones are obtained by the hydrolysis of the enol acetates. This transformation involves a 1,3-migration of the acetate to form pentadienyl cation and the formation of the gold carbene after a Nazarov-type cyclization. DFT calculations support this mechanism and provide interesting insight into the mechanism of the final stages of the process. 

Revision of Chapter 36. What would be the starting materials for the synthesis of these cyclopentenones by the Nazarov reaction and by the Pauson-Khand reaction Which do you prefer in each case - ... 

The short synthesis of (+)-frans-sabinene hydrate, an important flavor chemical found in a variety of essential oils from mint and herbs, was developed by C.C. Galopin. The key intermediate of the synthetic sequence was 3-isopropyl-2-cyclopentenone. Initially a Nazarov cyclization of a dienone substrate was attempted for the synthesis of this compound, but the cyclization did not take place under a variety of conditions. For this reason, a sequential Stetter reactionlintramolecular aldol condensation approach was successfully implemented. 

Ichikawa, J., Fujiwara, M., Okauchi, T., Minami, T. Fluorine-directed Nazarov cyclizations. Part 2. Regioselective synthesis of 5-trifluoromethyl-2-cyclopentenones. Syn/eff 1998, 927-929. 

Nazarov cyclization reaction. Synthesis of cyclopentenones by the acid-catalyzed electrocyclic ring closure of divinyl or allylvinyl ketones available by hydration of divinylacetylenes. 

Oppolzer,18 who wanted this cyclopentenone for the synthesis of modhephene 75 followed this strategy and found that the Friedel-Crafts went well with A1C13 as catalyst and the Nazarov cyclisation with another Lewis acid, SnCl4. You will notice the position of the double bond in the final product there are no protons on one side of the cation 73 so one must be lost from the other side. In cases where there is a choice, the more substituted alkene results, as here. The product is ideally functionalised for development into modhephene 75. 

A bis([2.2]paracyclophane)-annelated cyclopentadiene could be synthesized via a Nazarov cyclization of the bis([2.2]paracyclophane-l,9-dienyl) ketone 136 prepared by addition of monolithiodiene 133 to ethyl formate and subsequent oxidation of the carbinol 110. The synthesis was completed by diisobutylalumi-num hydride (DIBA1-H) reduction of the resulting cyclopentenone, and dehydration with p-toluenesulfonic acid. Treatment with methyllithium gave the corresponding cyclopentadienyllithium 136-Li, which was identified by NMR spec-... 

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