Tandem cyclic olefins

Grubbs has reported a similar tandem olefin metathesis-carbonyl olelination process for the preparation of cyclic olefins [31]. In this case, treatment of a keto-olefin with the molybdenum alkylidene 1 at 20°C generates an intermediate alkylidene complex. Under these conditions, competing intermolecular olelination does not occur. However, intramolecular carbonyl olelination of the initially formed alkylidene complex can occur and this results in the formation of a cyclic olefin. This tandem sequence is illustrated by the transformation of keto-olefins... 

More recently, the same principle was applied by the same authors to cyclic alkanes for catalytic ring expansion, contraction and metathesis-polymerization (Scheme 13.24) [44]. By using the tandem dehydrogenation-olefin metathesis system shown in Scheme 13.23, it was possible to achieve a metathesis-cyclooligomerization of COA and cyclodecane (CDA). This afforded cycloalkanes with different carbon numbers, predominantly multiples of the substrate carbon number the major products were dimers, with successively smaller proportions of higher cyclo-oligomers and polymers. 

As vinyl ethers were known to be poor substrates in Ru-catalyzed olefin metath-eses, it has been difficult to obtain cydic enol ethers by RCM of the vinyl ethers. Recently, a novel method to obtain cyclic enol ethers has been reported, which afforded cydic enol ethers directly from easily prepared dienes containing an allyl ether moiety [46]. Treatment of 70 with diene 99 in CH2CI2 in the presence of small amount of H2 resulted in a formation of dihydropyran 101 (Eq. 12.40). Treatment of 70 with H2 has been thought to produce an active catalyst for the olefin isomerization, and only metathesis products are formed until a small amount of H2 is introduced in the reaction. These results implied that this reaction most likely proceeded by way of a formation of the cyclic olefin 100, which was subsequently converted to dihydropyran 101 by the newly formed isomerization catalyst. In addition to the tandem reaction shown in Eq. 12.40, another method for obtaining cydic enol ethers from allyl ethers has also been demonstrated [46b]. This method induded addition of the hydride donor, such as NaBH4, to the reaction solution after the metathesis reaction had been completed. Although attempts to observe an active species for olefin isomerization in the presence H2 failed, these results suggested participation of hydride species in the olefin isomerization. 

Scheme 5.152 Tandem hydrofbrmylation-(Fischer indolization)-(Wagner-Meerwein-type rearrangement) reaction starting with cyclic olefins.

The tandem hydroformylation-Fischer indolization protocol was used in the synthesis of 2,3-disubstituted indoles. Several olefins, bearing substituents with various functional groups, as well as cyclic olefinic systems were investigated (Equations 7.20 and 7.21)... 

Zuercher WJ, Hashimoto M, Grubbs RH. Tandem ring opening-ring closing metathesis of cyclic olefins. J. Am. Chem. Soc. 1996 118 6634-6640. 

Preliminary investigations in this area involved treatment of olefinic ester 125 with a large excess (4 equiv) of the Tebbe reagent 93 (Scheme 18) [34a]. After 20 min at 25°C, the mixture was heated at reflux for 5 h. This resulted in the formation of tricyclic enol ether 127 in 71% overall yield. If only 1.3 equiv of Tebbe reagent 93 was employed and the reaction stopped after 20 min at 25°C,the olefinic enol ether 126 could be isolated in 77% yield. The proposed intermediacy of diene 126 in the initial tandem sequence was validated by its subsequent conversion into the cyclic enol ether 127 under the original reaction conditions [34a],... 

Tandem carbonyl olefmation—olefm metathesis utilizing the Tebbe reagent or dimethyl-titanocene is employed for the direct conversion of olefmic esters to six- and seven-mem-bered cyclic enol ethers. Titanocene-methylidene initially reacts with the ester carbonyl of 11 to form the vinyl ether 12. The ensuing productive olefm metathesis between titano-cene methylidene and the cis-1,2 -disubstituted double bond in the same molecule produces the alkylidene-titanocene 13. Ring-closing olefin metathesis (RCM) of the latter affords the cyclic vinyl ether 14 (Scheme 14.8) [18]. This sequence of reactions is useful for the construction of the complex cyclic polyether frameworks of maitotoxin [19]. 

Cycloisomerization represents another approach for the construction of cyclic compounds from acyclic substrates, with iridium complexes functioning as efficient catalysts. The reaction of enynes has been widely studied for example, Chatani et al. reported the transformation of 1,6-enynes into 1-vinylcyclopentenes using [lrCl(CO)3]n (Scheme 11.26) [39]. In contrast, when 1,6-enynes were submitted in the presence of [lrCl(cod)]2 and AcOH, cyclopentanes with two exo-olefin moieties were obtained (Scheme 11.27) [39]. Interestingly, however, when the Ir-DPPF complex was used, the geometry of olefinic moiety in the product was opposite (Scheme 11.28) [17]. The Ir-catalyzed cycloisomerization was efficiently utilized in a tandem reaction along with a Cu(l)-catalyzed three-component coupling, Diels-Alder reaction, and dehydrogenation for the synthesis of polycyclic pyrroles [40]. 

The tandem 0s04-catalyzed oxidative cleavage of olefin 269 with Oxone as the co-oxidant and sequential direct oxidation of intermediate aldehyde in alcoholic media led to cyclic keto lactone 270 in 45% yield (Equation 34) <20030L3089>. Similar oxidative cyclization with KMnCT-GuSITr resulted in 32% yield of 270 <1994T11709>. 

Grubbs reported tandem olefin metathesis/hydrogenation as a means to make satnrated cyclic prodncts and a one-pot RCM/transfer dehydrogenation/hydrogenation ronte to (R)-(-)-Mnscone utilizing (4a) (Scheme 19). Snapper and coworkers took advantage of the isomerization side reaction... 

Deprotonation of the unsaturated diester with sodium methoxide leads to a stabilized anion that undergoes effective [3 + 2] cycloaddition to electron-deficient olefins (cyclic and acyclic) via tandem Michael additions15. The product is formed in moderate to good yield, with the stereochemistry often reflecting the thermodynamic preference. 

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). ... 

In the present wcffk, proton and carbon-13 nuclear magnetic resonance (% H . and i ) spectroscopy are used in tandem to acconplish the original goal of the chemical methods, namely, determination of the nature and level of the remaining olefinic unsaturation in order to determine cyclicity (as well as bo yield other micros tructural information). This >proach has not been reported for cyclized polyisoprene althou essentially (infrared spectroscopy plays the role pl ed by IWR in our work) the approach has recently been reported for cyclized polybutadiene. 

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