Olefins strained

The following compounds have been obtained from thiete 1,1-dioxide Substituted cycloheptatrienes, benzyl o-toluenethiosulfinate, pyrazoles, - naphthothiete 1,1-dioxides, and 3-subst1tuted thietane 1,1-dioxides.It is a dienophile in Diels-Alder reactions and undergoes cycloadditions with enamines, dienamines, and ynamines. Thiete 1,1-dioxide is a source of the novel intermediate, vinylsulfene (CH2=CHCH=SQ2). which undergoes cyclo-additions to strained olefinic double bonds, reacts with phenol to give allyl sulfonate derivatives or cyclizes unimolecularly to give an unsaturated sultene. - Platinum and iron complexes of thiete 1,1-dioxide have been reported. 

The reaction of perfluoroalkyl iodides with electron donor nucleophiles such as sodium arene and alkane sulfinates in aprotic solvents results in radical addition to alkenes initiated by an electron-transfer process The additions can be carried out at room temperature, with high yields obtained for strained olefins [4 (equations 3-5)... 

Furthermore highly strained compounds such as bicyclo[3.2.1]oct-l-ene 11, containing a double bond to a bridgehead carbon atom, have been prepared however this strained olefin could be identified only as its Diels-Alder product from subsequent reaction with an added diene." ... 

Dittmer and Christy64 studied the reactions of thiete sulphone. Included in these was an attempt to synthesize thiete itself, a highly strained olefin of theoretical interest, by the LAH reduction of thiete sulphone. The reduction was expected to be feasible since Bordwell and McKellin63 had found that thietane sulphone was readily reduced, but the only product that Dittmer and Christy isolated was 1-propanethiol (equation 23). Reduction of the thiete sulphone with sodium borohydride in basic aqueous methanol gave a 61% yield of the saturated ring, thietane sulphone. 

New kinds of living polymer systems result from the reactions of transition metals with cyclic, strained olefins 16). These polymerizations proceed through the intermediacy of metal carbenes and are exemplified by the polymerization of norbomene initiated by bis(cyclopentadienyl)-titane-cyclobutane described recently by Grubbs17>. 

Scheme S3 Plausible mechanism for catalytic episulfidation of strained olefins by the use of Mo(0)(S2)(S2CNEt2)2...

Reactive unsaturated nitroso compounds such as 1112 can also be readily prepared from a-halooximes such as 1111 on treatment with powdered Na2C03 in diethyl ether to give, in the presence of enoltrimethylsilyl ether 1113 or strained olefins such as norbomene and other dienophiles, hetero-Diels-Alder adducts such as 1114 and 1115 in moderate yields [150-155] (Scheme 7.47). 

The intermediate formation of a dianthracene derivative was utilized in the synthesis of the highly strained olefin 9,9 -dehydrodianthracene,<37)... 

The reason for this behavior can be seen in the structure of the intermediate biradical. The rigidity of the cyclobutyl ring prevents a parallel alignment of the p orbitals with the 0 bond, which is held practically perpendicular. In order for type II cleavage to occur, an initially severely strained olefin must be formed. Hence radical recombination to yield the bicyclopentane system predominates. 

Rh2(OAc)4 is the most effective and versatile of the three catalysts used. Terminal and non-terminal olefins, strained olefins (norbomene, norbomadiene) and conjugated olefins (styrene) all react in good yield. 

As in the case of dimerizations, MCP derivatives are known to undergo metal-catalysed [2 + 2] codimerizations with other alkenes in a few cases [2]. The examples are limited to strained olefins, such as norbornadiene (572) (Scheme 79) [152] and cyclobutene (574) (Scheme 80) [153], and to alkyl acrylates (Table 46) [154] and always compete with the alternative [3 + 2] addition of TMM species. 

Some of these coupling reactions can be made catalytic if hydrogen is eliminated and combines with the anion, thus leaving the nickel complex in the zero-valent state. Allylation of alkynes or of strained olefins with allylic acetates and nickel complexes with phosphites has been achieved (example 38, Table III). 

Oxidation of carbon ligands with concomitant insertion has been observed in the reaction of methallyl nickel complexes with norbornene or strained olefins in general and oxygen (example 3, Table IX). 

This process is of a rather general character, and different types of olefins, such as normal olefins, Michael substrates, inverted and strained olefins, can be involved in such reactions. However, the interaction shown in Scheme 3.131 is accompanied by a number of side reactions, and consequently, the scope of the transformation (161 162) and the yield of nitrosoacetals (162) substantially depend on the nature of the substituent R. 

Luef, W., Strained Olefins Structure and Reactivity ofNonplanar Carbon-Carbon Double Bonds, 20, 231. 

The alkyl-substituted titanium carbene complex 18 reacts with norbornene 24 to form a new titanacycle 25, which can be employed for the ROMP of 24 (Scheme 14.13). The titanacycle generated by the reaction of the Tebbe reagent with 24 is also used as an initiator for the same polymerization [23]. These preformed titanacyclobutanes also initiate ROMP of various other strained olefin monomers [24],... 

After its discovery the method was affected by various problems. For instance, a stoichiometric amount of catalyst and the use of strained olefins were necessary to obtain useful yields. Furthermore, if unsymmetrical alkynes and alkenes were used, the reactions typically gave a mixture of re-gioisomers. In addition, many early examples reported the need for long reaction times and high temperatures to obtain full conversion. 

An important advance was reported by Schore and Croudace [13], who showed for the first time that carbon-tethered enyne precursors undergo an intramolecular Pauson-Khand reaction (PKR) in good yields with complete control of regioselectivity. In this connection, it was not essential to use strained olefins as starting materials. 

Tetrasubstituted twisted ethylenes have become of much interest, partly because of the advent of new synthetic methods (184,185) suitable for the preparation of highly strained olefins. However, the most interesting target, tetra-rm-butyl-ethylene (130a) eludes investigators. It has been the object of several force-field calculations with somewhat varying outcomes. Ermer and Lifson (176,186) cal-... 

The intermolecular carbocyclization with a strained olefin, such as norbornene 35, has been frequently used for proof-of-prindple in challenging metal-catalyzed transformations. The use of rhodium catalysts fadhtates the intermolecular reaction, albeit in modest yield and with poor regioselectivity (Scheme 11.10). Ethylene 39 can also be utilized to this end, but generally affords the carbocydization products in low yield, as... 

Scheme 11.10 Intermolecular PK reactions with strained olefins and ethylene.

The copolymerisation of CO and strained olefins such as norbornene and norbor-nadiene is effectively catalysed by Pd complexes with both phosphines and chelating diphosphines [43-49]. As previously mentioned, many model studies aimed at elucidating the elementary steps of alkene/CO copolymerisation have made use of cyclic alkenes in aprotic media because the products resulting from the insertion of... 

The polymerization of cyclic, strained olefins by transition metal alkylidenes of general formula L M = CRR (L = ligand, R, R = H, alkyl, aryl) yields polymers formed via ring-opening that contain unsaturated double bonds within each repetitive unit. Since the mechanism is based on repetitive metathesis steps, this polymerization reaction is known as ring-opening metathesis polymerization (ROMP) (Scheme 1). 

The higher reactivity of ring-strained olefins has been exploited by several workers in 1,3-dipolar cycloaddition reactions of milnchnones. Thus, Kato and co-workers (112) reported that miinchnone 38 reacts with 1,2,3-triphenyl-1//-phosphirene (202) to give l-methyl-2,3,4,5-tetraphenylpyrrole (203) (45% yield). Control experiments demonstrated that phosphirene 202 does not decompose to diphenylacetylene appreciably under the reaction conditions. Moreover, the reaction of diphenylacetylene and miinchnone 38 afforded only a 21% yield of pyrrole 203. 

Other tris(olefin)platinum(0) complexes (where olefin represents a strained olefin such as bicyclo[2.2.1]heptene, dicyclopentadiene, or trans-cyclooctene) may be similarly obtained by direct displacement of 1,5-cyclooctadiene, often in quantitative yield.6... 

However, from the outset of this field, the limitations as well as the potentials of this cycloaddition were also apparent. For instance, the efficiency of this cycloaddition in an intermolecular manner was typically low unless strained olefins were used. Moreover, the use of unsymmetrical alkenes led to a mixture of the cyclopentenone regioisomers. Synthetic utility of this reaction is considerably expanded by the emergency of the intramolecular reaction. Schore introduced the first intramolecular version forming several rings simultaneously, which is now the most popular synthetic strategy in natural product synthesis because of its conceptual and operational simplicity. Additionally, the regiochemistry is no longer the problem in this variation. 

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