Cyclopentene annelation

Cyclopentene annelation.1 The reaction of the anion of a 1,3-dicarbonyl compound with l-decynyl(phenyl)iodonium tetrafluoroborate results in an annelated 3-pentylcyclopentene in reasonable yield. The product is considered to result from... 

This [3 + 2]cyclopentene annelation has been used to obtain the sesquiterpene pentalenene (6) from the enone 2.2 Reaction of 2 with the dienolate 1 provides the... 

Cyclopentene annelation. The known rearrangement of vinyl cyclopropanes to cyclopentenes (cf. 7, 190 9, 83, 265) can be used to obtain silyl-substituted cyclopentenes. The precursors, (l-trimethylsilylcyclopropyl)ethylenes (2), are usually prepared by addition of 1 to an aldehyde or a ketone followed by cyclopropanation (C2HjZnI, CH2I2) of the adduct. The products are then dehydrated by TsOH to 2 (equation I).1... 

Cyclopentene annelation by (3 + 2] cycloaddition.1 A key step in a synthesis of the alkene 6 is the cycloaddition of I to 2,3-dicarbomethoxynorbornene (2) catalyzed by tetrakis(triisopropyl phosphite)palladium(0). The product (3) was converted to the... 

A similar intermolecular cyclization was recently utilized in the synthesis of highly substituted dihydropyrrole derivatives [133 -135]. In a specific example, the addition of pentadienyltosylamide derivatives 177 to propynyl(phenyl)iodo-nium triflate initiates a sequence of transformations that furnishes the complex, highly functionalized cyclopentene-annelated dihydropyrrole products 178 in moderate yields with complete stereoselection (Scheme 66). Under similar reaction conditions, the isomeric isoprene-derived tosylamide 179 reacts with propynyl(phenyl)iodonium triflate to give azabicyclo[3.1.0]hexane 180 as the final product [134]. 

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. ... 

The reactions of sterically encumbered allenylsilanes of structure type (66) with iV-acyliminium ions generated by the titanium tetrachloride promot reaction of ethoxypyirolidinone produced the nitrogen heterocycle (70), as depicted in Figure 13. In this reaction it is likely the lactam product is generated by a pathway similar to that involved in the [3 + 2] cyclopentene annelation. Thus, a regiospecific electro-... 

Cyclopentene ring from vinylcyclopropanes Stereospecific cyclopentene annelation... 

Addition of organocuprate reagents to a,j8-enones is solvent dependent indeed the addition is retarded by the inclusion of HMPA in the reaction medium to the extent that halide-ion displacement occurs preferentially. " Copper-catalysed conjugate addition of the magnesio-acetal (25) to cyclic enones is the key step in a new cyclopentene annelation procedure [equation (36)]. ... 

Interesting is the finding that the cyclopentene annelation does not cause a large difference in the a values for azoalkane 5b compared to 17 cf. Table 93.2). Evidently, the annelated cyclopentene ring in the bicycHc 5d is sufficiently distant from the reaction site such that it exercises little influence on the skeletal inversion process. 

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