Cyclopen tenes synthesis

Carbon radical generation. Radicals that are formed during dehalogenation can be intercepted intramolecularly by a C=C bond " or C=N bond. A cyclopen-tene synthesis from 1,1-dihaloalkenes apparently involves two-stage reduction, which is intervened by hydrogen abstraction. 

Madindoline A (7) and B (ent-8) are potent inhibitors of interleukin 6. In a total synthesis [21] that also intended to determine the relative and absolute configurations of these novel antibiotics, the densely functionalized cyclopen-tene-l,3-dione ring of 7 and 8 was elaborated via RCM of diene-diol 2 (Scheme 1). 

Crimmins, M. T. Tabet, E. A. Formal total synthesis of (+)-trehazolin. Application of an asymmetric aldol-olefin metathesis approach to the synthesis of functionalized cyclopen-tenes./. Org. Chem. 2001, 66, 4012-4018. 

An improved version of the Carroll reaction, the ester enolate Carroll rearrangement, was reported in 1984 by Wilson and Ptice. Dianions of allylic acetoacetates, generated by treatment with 2 equiv. of LDA at -78 °C in THF, were rearranged at room temperature or 65 C to yield >keto acids in 40-80% yield (equation 12). In the course of a synthesis of the sesquiterpene isocomene, Snider and Beal used this method for the rearrangement of acetoacetate (73), prepared in 83% yield from reaction of cyclopen-tene (72) with diketene and a catalytic amount of DMAP (Scheme 11). The ( )-isomer of ketone (74) is obtained stereospecifically, since there is a severe steric interaction between the methyl groups in the Carroll rearrangement transition state leading to the (Z)-isomer. 

Since our direct route to angularly fused triquinanes from cycloaddition of l-(4-pentynyl)cyclopen-tenes is limited to trisubstituted alkenes and simple terminal alkynes, bisnorisocomene, but not iso-comene itself, could be prepared (Scheme 22). However, this limitation is not a factor for most other compounds in this class of natural products, and the steric interactions described earlier worked to our advantage in a diastereocontrolled synthesis of pentalenene (see structure. Scheme 20). The natural product was obtained by subjecting the product of Scheme 14 to the sequence i, Li, NH3, MeOH ii, MeLi, Et20 iii, p-TsOH, benzene, reflux. ... 

Lewis acid catalysis of the vinylcyclopropane rearrangement has been reported for vinylcy-clopropane 3, a key intermediate in the synthesis of the plant hormone antheridogen-An. Most recently, a report has appeared describing a highly stereoselective, diethylaluminum chloride promoted rearrangement of vinylcyclopropanes 5 to cyclopentenes 6. The cyclopen tenes appear to be formed directly, in some cases as a consequence of the rhodium-promoted cyclopropanation of enol ethers (see Section 2.4.3.1.3.). ... 

Cyclic (hetero- and carbocyclic) vinyl sulfoxides have been prepared by a tandem Michael addition/Homer olefination reaction of a-phosphorylvinyl sulfoxides and carbonyl compounds bearing a nucleophilic center. Using optically active a-phosphorylvinyl sulfoxides a series of enantiomeric cyclic vinyl sulfoxides in which the chiral sulfinyl group is bonded to a chromene, pyrrazolyne, quinoline or cyclopen-tene ring, has been obtained. The H-W-E reaction of aldehydes with sulfinimine-derived 3-oxo pyrrolidine phosphonates (228) represents a new method for the asymmetric synthesis of ring-functionalized cw-2,5-disubstituted 3-oxo pyrrolidines (229) (Scheme 90). ... 

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