Cyclopentanone annelation

Cyclopentanone annelation. a,a-Dichlorocyclopentanones, obtained by addition of dichlorokctcnc to cycloalkcnes followed by ring expansion with diazomethane (9, 133-134), are versatile intermediates to a variety of interesting products. Some of the transformations are indicated in Scheme (I) and equation (I).1... 

Cyclopentanone annelation (10, 139-140) - The iterative cyclopentenone anne-lation has been extended to a synthesis of hirsutic acid (7) starting with the ester I. This alkene surprisingly does not react with chloromethylketene, but does react stereoselectively with dichloroketene to give 2 as the major product One of the chlorine atoms was replaced by methyl by treatment with (CH,) CuLi (3 equiv. ) and then with CH,I and HMPT. Ring... 

Triethylamine Cyclopentanone ring from 1-cyclopropylenoxysilanes Cyclopentanone annelation... 

Cyclopentanone annelation via thermolysis of trimethylsilyl enol ethers of cyclopropyl methyl ketones has been studied a good yield of bicyclo[5,3,0]decan-8-one was obtained from (321 R = Q=CH2)OSiMe3 R = H), but only a low yield of bicyclo[5,3,0]decan-9-one was obtained from [321 R = H, R = C(=CH2)-... 

OSiMe3]. Acid-catalysed decomposition of p,y-unsaturated diazomethyl ketones has been developed as a cyclopentanone annelation procedure, thus (322) gave 10,10-dimethylbicyclo[5,3,0]dec-7-en-9-one (50—69%) when treated with BFa-etherate then aqueous HCl. The enolate anion of 2-methoxycarbonylcycloheptanone reacts with 1-phenylthiocyclopropyltriphenylphosphonium fluoroborate to give the Wittig product (323) which was hydrolysed to the corresponding keto-acid (90% overall). 

Numerous attempts to obtain pyrroles annelated with a cyclopentane ring, starting from cyclopentanone oxime, were unsuccessful. Despite widely varying conditions, it was possible to detect (by NMR or IR spectroscopy) only trace amounts of pyrroles in the products (84MI1). 

Methyleneeyclopentane annelation (9,454-455). The mesylate (2) of 1 has been usedasan electrophilic equivalent of trimethylenemethane for methyleneeyclopentane annelation of a cyclopentanone in a synthesis of coriolin (7).2 Thus, reaction of the enolate of 4, a protected equivalent of 3, reacts with 2 to give 5, which after oxidation to the disulfone is cyclized by fluoride ion to the tricyclic methyleneeyclopentane derivative 6. The product is converted into 7 by several known transformations. 

Phenol annelation.1 This modified methyl vinyl ketone can be used for synthesis of 5,6,7,8-tetrahydro-2-naphthol or 5-indanol by reaction with the lithium enolate of cyclohexanone or cyclopentanone, respectively. The former reaction is formulated in equation (I). 

Annelation. Cleavage of l-(trimethylsilyloxy)-2-alkoxycarbonylcyclo-propanes (1) with KF-18-crown-6 generates y-oxo-a-ester enolate anions, which can be trapped by electrophiles. Trapping with a vinyl phosphonium salt results in [3 + 2] annelation to provide annelated cyclopentanones (2).1... 

The thermal C3 -> 5 ring expansion of 1-siloxy-l-vinylcyclopropanes occurs either from the Z or from the E isomers. It leads to cyclopentanone silyl enol ethers that are able to undergo either further regiospecific alkylation into 2,3-disubstituted cyclopenta-nones 145.209,213 dehydrosilylation into cyclopentenones The overall process constitutes an efficient three-carbon annelation process (equation 129). 

X -.".e third case, cyclopentanone has self-condensed and ignored the enone to which it was to add in a conjugate fashion and continue with a Robinson annelation (p. 761). The liiis - - again is to use a specific enolate such as an enamine though the simplest here is a keto-ester can be easily prepared by intramolecular Claisen ester condensation (p. 727). 

Both cyclic and acyclic enone systems participate in the (trimethylsilyl)cyclopentene annelation (Table 6). a-Methylene ketones react to form spiro-fiised systems and the intermediates derived from ace-tylcyclohexanone, cyclohexenone and cyclopentanone cyclize to yield S,S- and 6,3-fiised ring systems. ... 

Cyclopeutanoues, Jung and Hudspeth have devised a new cyclopentanone synthesis by three-carbon annelation of an alkene via a Diels-Alder reaction. They chose the dimethoxytetrachlorocyclopentadiene 1 as the diene component because it is remarkably reactive. The general method is outlined for methyl acrylate (2, equation I). The chlorine atoms of the adduct 3 are replaced by... 

In the third case, the cyclopentanone has self-condensed and ignored the enone. The answer again is to use a specific enolate, such as the easily made P keto-ester below. The six-membered ring is then easily formed by intramolecular aldol reaction. These two reactions together make a Robinson annelation. Finally the C02Me group must be removed by hydrolysis and decarboxylation. 

Annelation. This reagent reacts slowly, but in high yield, with cyclohexanone and cyclopentanone to form a tertiary alcohol. The annelation of cyclohexanone to form A -octalone is illustrated (equation I). This annelation differs from a Robinson annelation in that the 3-ketobutyl group is introduced at the site of the carbonyl group rather than in the a-position. ... 

Cycloaddition reactions between alkenes and the very reactive diene (34) lead to adducts of the type (35), which can be converted into cyclopentanones following reduction to (36), oxidative cleavage of the double bond in (36), and decarboxylation of the resulting /3-keto-acid (Scheme 9). The four-stage sequence amounts to a three-carbon annelation reaction, and overall yields are of the order 20—40%. 

Silyldienals result from Me3SiC CH2Br and silyl substituted polyenes used to make di and triquinanes, cyclopentanes, and and monosilylated dienyl and trienylsulphides, and tetraenesl H, while enones are used in annelation reactions and in cyclopentanone synthesisl l. Silylated bromobutenes give bicyclo[1.1.0]butanes, (Me3SiCH2CH=CH-)2... 

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