Vinylcyclopropanes cyclic

The rearrangement proceeds from the Si-state of the 1,4-diene 1. The Ti-state would allow for different reactions like double bond isomerization. Rigid systems like cyclic dienes, where EfZ -isomerization of a double bond is hindered for steric reasons, can react through the Ti-state. When the rearrangement proceeds from the Si-state, it proves to be stereospecific at C-1 and C-5 no -isomerization is observed. Z-l,l-Diphenyl-3,3-dimethyl-l,4-hexadiene 5 rearranges to the Z-configured vinylcyclopropane 6. In this case the reaction also is regiospecific. Only the vinylcyclopropane 6 is formed, but not the alternative product 7. ... 

Stansbury and Bailey. A review by Colombam on addition-fragmentation processes is also relevant. Monomers used in ring-opening are typically vinyl (e.g. vinylcyclopropane - Scheme 4.20 Section 4.4.2.1) or methylene substituted cyclic compounds (e.g. ketene acetals - Section 4.4.2.2) where addition to the double bond is followed by p-scission. 

The photoindueed 1,7-cycloaddition of carbon monoxide across the divinyl-cyclopropane derivative 32 yields the two cyclic dienyl ketones 34, via the ferracyclononadiene intermediate 33 [18]. (Scheme 11) cyclopentene rearrangement. The dienylcyclopropane 35 is capable of forming the complex 36, followed by ring enlargement to 37 [19]. 1,1-Dicyclopropylethylene 29 is also converted to the 1-cyclopropyl-1-cyclopentene 38. The additional functionality of vinylcyclopropanes is necessary to serve as a 7t-donor... 

When vinylcyclopropane is used as the key reference compound, the only examples of significant bond (electron) delocalization energies are cyclic homoconjugative systems with potentially aromatic electron ensembles (compare compounds 27-38 in Table 2). For example, norcaradienes 33 and 34 possess small, but significant bond delocalization energies RE of about 3 kcal mol1 (Table 2). Similarly, the RE values of the cyclohepta-trienes 30,31 and 32 are between 4 and 6 kcal moT1. 

Numerous examples of vinylcyclopropane to diene rearrangement have been studied (e.g. equation 134)178 and thoroughly reviewed in the aforementioned surveys and in this series , and hence will not be repeated here. The reader will also find in this series180 ample examples of typical ring-opening reactions of cyclic vinylcyclopropanes (equation 135)181... 

Mild Ni(0)-catalysed rearrangements of l-acyl-2-vinylcyclopropanes to substituted dihydrofurans have been developed.86 The room temperature isomerizations afford dihydrofuran products in high yield. A highly substituted, stereochemically defined cyclopropane has been employed in the rearrangement to evaluate the reaction mechanism. The Cu(II)-catalysed cycloisomerization of tertiary 5-en-l-yn-3-ols with a 1,2-alkyl shift affords stereoselectively tri- and tetra-cyclic compounds of high molecular complexity (Scheme 29).87 A proposed mechanism has been outlined in which... 

The reaction of racemic 147 with (R)-carvone, initially at -78 °C followed by warming to room temperature for 1 h, gave the vinylcyclopropane 151 in 72% yield and moderate diastereoselectivity (d.r. = 75 25). The stereochemistry of the major diastereoisomer shown in structure 151 from H NMR studies was that expected based on the stereochemical outcome of the reaction of racemic 147 with the achiral cyclic enones 146 and is consistent with our previously proposed chelated transition state90 for cyclic enones (compare with the transition state B). 

Corey and Wollenberg have found it possible to introduce a THP-blocked trans allylic alcohol unit via reaction of 2-cyclopentenone and other cyclic enones with the highly reactive mixed cuprate 28.58 Through hydrolysis, mesylation, and base-promoted cyclization of adduct 29, the vinylcyclopropane 30 was obtained (Scheme 8). Thermolysis at 600 °C caused ring expansion to 31. 

The intermolecular addition of carbamates to 1,3-dienes (equation 147) under mild conditions has been described as well. The hydrothiolation of 1,3-dienes has also been reported. " Other related conjugate additions can be performed over methylenecyclopropanes (equation 148) with sulfonamides and the resulting product cyclizes by a second hydroamination of an olefin, finally yielding cyclic sulfonamides. This behavior is reproduced in a similar reaction for the ring opening of vinylcyclopropanes with sulfonamides. One more example in this group of reactions is the synthesis of dUiydrobenzofurans from aryl-allyl ethers. ... 

With regard to the reagents used in this type of cyclopropanation, 1,2-dibromoethane has been used most frequently. l-Bromo-2-chloroethane, however, may give better yields in some cases. 2-Chloroethylsulfonium iodide is used in the reaction of cyclic ketones to give the spiro derivatives . The use of vinylogous derivatives of 1,2-dihalides allows a synthesis of vinylcyclopropanes (equation 89) . (Chloromethyl)oxirane provides substituted cyclopropylmethanols (equation Oxiranes may also be used in place of... 

The pyrrolidine enamines of cyclopentanone (552a) and cyclohexanone (552) undergo exclusive 1,7-addition with the vinylcyclopropane 528 yielding 566. Mild acidic hydrolysis yields 2-substituted cyclic ketones (567) (equation 198). ... 

Use of ( )-l,4-dibromobut-2-ene in the SIRC reaction gives rise to vinylcyclopropanes (Table 7). The cyclopropanation is induced by bases such as sodium ethoxide, sodium hydride or sodium amide or can be carried out under phase-transfer conditions. The reaction is non-stereoselective however, a diastereomeric excess of 39-80% was obtained with nucleophiles containing a chiral auxiliary. When cyclic ketones are used as nucleophiles, spiro-cyclo-propanes, which serve as precursors for (Z)-jasmonate or methyl jasmonate (Table 7, entries 5-7), are formed. 

In contrast to acyclic 1,4-dienes, which rearrange to vinylcyclopropanes from the excited singlet state vide supra), cyclic 1,4-dienes usually undergo the di-7i-methane rearrangement from the triplet state.Bicyclo[3.1.0]hex-2-enes (2, n = 1) and bicyclo[4.1.0]hept-2-enes (2, n = 2) are thus obtained from eyelohexa-1,4-dienes and eyclohepta-1,4-dienes, respectively. 

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