Furans cyclopropyl ketones

Transformation of pyridazine 1-oxides and their methyl derivatives into cyclopropyl ketones and/or substituted furans can also occur (Scheme 14). 

Another example of Au-catalyzed was reported using alkynyl cyclopropyl ketones as a starting material. Trisubstituted furans were given in high yields under mild condition via a domino reaction process and an example is given below <06AG(I)6704>. 

Similarly, carbinols 237 are converted to dienes 238 having two benzenethio substituents (Scheme 11)101). Here again starting materials are dichloro-cyclopropyl ketones 235 (cf. Scheme 5), which can be transformed to the desired dithioacetals 236 by treatment with sodium benzene thiolate. Cyclopropanes 236 are ring opened to P,y-unsaturated ketones 240, y-oxothioesters 241, or for R1 = H expanded to furan derivative 239102 t03>. 

Depending upon reaction conditions, the Pd-catalysed isomerisation of alkylidene cyclopropyl ketones can lead to furans or pyrans. In acetone and in the absence of added salts, proximal bond cleavage occurs exclusively and 4//-pyrans are formed <03AG(E)183>. The 4//-pyran unit has been spiro-linked into the indanoparacyclophanes <03T1739>. 

Photocyclisation of 8-alkoxy-l,2,3,4-tetrahydro-l-naphthalenones and 4-alkoxy-6,7,8,9-tetrahydro-5H-benzocyclohepten-5-ones gives naphtho[l, 8-bc]furans and cyclohepta[cd]benzofurans respectively, and conformational and substituent effects of 1,5-biradicals in the cyclisation process are discussed." " The same authors also describe substituent effects on the photocyclisation of ethyl 2-(8-oxo-5,6,7,8-tetrahydro-l-naphthyloxy)acetates and ethyl 2-(5-oxo-6,7,8,9-tet-rahydro-5H-benzocyclohepten-4-yloxy)acetates to give naphtho[l,8-bc]furans and cyclohepta[c,d]benzofurans respectively." Also reported are cyclisations involving photogenerated radical cations of unsaturated silyl enol ethers, fragmentation cyclisations of unsaturated ot-cyclopropyl ketones which occur by photoelectron transfer and give polycyclics, and kinetic and theoretical studies of [2+3] cycloadditions of nitrile ylids. These reactions have been studied mechanistically and their synthetic potential investigated. 

The halopalladation of MCPs gives CP-Pd and CPC-Pd intermediates depending on the reaction conditions. Thus, the isomerization of alkylidene cyclopropyl ketones to 4ff-pyran derivatives takes place in the presence of a palladium chloride catalyst via chloropalladation to form a CPC-Pd and the successive P-carbon elimination (Eq. 10) [25]. In contrast, the addition of Nal changes the reaction pathway dramatically. Under the conditions, the reaction proceeds through a CP-Pd intermediate and results in the formation of furan derivatives. 

Substituted furans are important structural imits, which are often seen in natural products or pharmaceuticals. Hashmi and his colleagues have found that 2-substituted furans are formed from aUenyl ketones by gold-catalyzed cycloisomerization [ 197]. Halofurans and highly substituted furans can be also prepared according to this strategy [198, 199]. Gold(III) porphyrin complexes have been developed as recyclable catalysts for the cycloisomerization [200]. 2-(l-Alkynyl)-2-alken-l-ones [201], l-(l-alkynyl)-cyclopropyl ketones [202], and (Z)-2-alken-4-yn-l-ols [203] are also suitable substrates for highly substituted furans. 

Carbonylation of l-(l-alkynyl)cyclopropyl ketones in the presence of a rhodium(I) catalyst yielded 5,6-dihydro-4//-cyclopenta[c]furan-4-ones via cleavage of the cyclopropane C-C bond (Scheme 2.86) [140]. Initial cleavage of the more congested C-C bond, generating a rhodacyclobutane, was proposed as an explanation of product formation. 

A related synthesis of highly substituted furans was reported by Schmalz and Zhang from cyclopropyl alkynyl ketones. The reaction scope included a great variety of nucleophiles such as several alcohols, indole or even acetic acid [140]. 

Ethen 1 -Cyclopropyl-1 -morpholino-E15/1, 616 (Keton + Amin) Furan 3-(2-Cyan-ethyl)-3,4-... 

Nicotine has been prepared in one step by ring expansion of cyclopropyl 3-pyridyl ketone Phthalimidines can be obtained by intramolecular Friedel-Crafts ring closure of carbamyl chlorides . Easy preparations of 2-methylindoles from ar. amines and 2,3-dibromopro-pene through N-(2-bromallyl)anilines and of 1-azaadamantanes from N-tosylpiperidone enamines through 3-azabicyclo[3.3.1]non-9-ones have been reported. 3-Hydroxypyridinium salts have been prepared by a new method, the chlorine oxidation of N-monosubst. 2-(a-amino-alkyl)furans . 

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