Thermal addition

Cyclopentadiene oligomers have been formed by vapor deposition of CPD on kaolin to afford a sorbant for removal of oil from water (71). They are also employed as coatings for controlling release rates of fertilizers (72). Thermal addition of sulfur to a mixture of DCPD and CPD oligomers has led to a number of beneficial appHcations such as waste water oil adsorbant powdery foams (73), plasticized backing for carpets and artificial turfs (74), and in modified sulfur cements for encapsulating low-level radioactive wastes (75). 

Examples of perfluoroalkyl iodide addition to the triple bond include free radical addition of perfluoropropyl iodide to 1 -heptyne [28] (equation 21), thermal and free radical-initiated addition of lodoperfluoroalkanesulfonyl fluorides to acetylene [29] (equation 22), thermal addition of perfluoropropyl iodide to hexa-fluoro 2 butyne [30] (equation 23), and palladium-catalyzed addition of per-fluorobutyl iodide to phenylacetylene [31] (equation 24) The E isomers predominate in these reactions Photochemical addition of tnfluoromethyl iodide to vinylacetylene gives predominantly the 1 4 adduct by addition to the double bond [32] Platinum catalyzed addition of perfluorooctyl iodide to l-hexyne in the presence of potassium carbonate, carbon monoxide, and ethanol gives ethyl () per fluorooctyl-a-butylpropenoate [JJ] (equation 25)... 

The ene reaction as a reaction principle has been first recognized and systematically investigated by Alder It is a thermal addition reaction of a double bond species 2—the enophile—and an alkene 1—the ene—that has at least one allylic hydrogen. The intramolecular variant is of greater synthetic importance than is the intermolecular reaction. 

The thermal addition of dimethyl acetylenedicarboxylate to indoles, unlike the photocycloaddition (see Section 3.2.1.4.1.1.), proceeds via a polar stepwise process to yield, initially, 3,4-benzo-2-azabicyclo[3.2.0]hepta-3,6-dienes which in some cases are isolable,13 141 but which, in general, ring open in situ to give the indolylacrylates 3 and/or undergo electrocyclic ring expansion to 1-benzazepines.21... 

Sulfonyl bromides and iodides react similarly217-218-225 copper-salt catalysis in these cases facilitates the additions but is not absolutely necessary however, it influences the stereochemistry of the additions. Addition of sulfonyl iodides226 as well as the uncatalyzed thermal addition of sulfonyl bromides227 to alkynes leads to an exclusive trans-addition, whereas CuBr2 catalysis in the latter case causes the formation of cis-addition products to some extent (11 16%) correspondingly, copper-salt catalysis in sulfonyl chloride additions to alkynes leads to the formation of a mixture of Z,E-isomers228-229 (equation 40). 

In the thermal reaction of aliphatic and aromatic sulfonyl chlorides with acetylenes no adduct has been observed82. However, the light-catalyzed additions of sulfonyl iodides to acetylenes83 as well as the thermal addition of sulfonyl bromides to phenylacetylene84 to form 1 1 adducts have been shown to be stereoselective and to occur in good to excellent yields. The fact that the addition occurs in a trans manner forced the authors83,84 to suggest that chain transfer by the sulfonyl halide (k ) is much faster than isomerization of the intermediate vinyl radical (k2) (see Scheme 5). 

The suprafacial thermal addition of an allylic cation to a diene (a [3 -f- 4] cycloaddition) is allowed by the Woodward-Hoflfmann rales (this reaction would be expected to follow the same rules as the Diels-Alder reaction ). Such cyclo-... 

The a-n interaction in the excited-state n electron systems is also successfully treated. The 1,2-addition will take place with cis mode as is indicated in Fig. 7.39. This was predicated in reference B6>. Experimental evidence 64>149> is the photoinduced addition of IV-chlorourethane to olefins which gives mainly cis addition product, while thermal addition produces a dominantly trans adduct. 

Endo product (86) is thought to result from thermal addition and is probably not a photoproduct. Cyclohexadiene yields cyclobutanes (87)—(89) and 1,4-cycloaddition product (90) with dimethylmaleic anhydride(87> ... 

As proposed S-14 is a very reactive electrophile, as demonstrated, firstly, by the thermal addition of nitrogen at 25 K to give 13 back, secondly, by the addition of CO to yield 2i/-imidazol-2-ylideneketene (15) (T-10 reacts in a similar fashion31), and thirdly, by formation of a complex 14-Xe of the carbene with xenon. In a xenon matrix complexes of this type were also found by Sander et al.37 for difluorovinylidene and by Maier and Lautz38 for C2. 

Compounds having an As-Se bond undergo thermal addition to phenylacetylene at 80 °C to give ( )-adducts, with the Se group attached at the terminal carbon (Equation (132)).300... 

Mare, P. B. D. de la Kinetics of Thermal Addition of Halogens to Olefinic... 

Thermal addition of hydroxylamines to non-activated C=C bonds has been observed only during cyclization processes The reaction proceeds through a thermal retro-Cope mechanism as evidenced by its suprafacial stereospecihcity (equation 37). ... 

The ene-reaction, which is mechanistically related to the Diels-Alder reaction, has also been reported. The thermal addition of 3-ferf-butoxycarbonyl-2(3//)-oxazolone 236 to 2,2 -biindole 235 affords 4-(2,2 -biindol-3-yl)-2-oxazolidinone 237, probably via the indoline derivative. The product is further converted to the fused aromatic compound 238 by bromination with NBS and AIBN, followed by dehydrobromination (Fig. 5.58). ... 

Fig. 9. Frontier orbital mixing for the thermal addition of 1,3-butadiene to V-methyl-quinolinium-3-olate (467 -> 468).

Cyclopentenes behave differently and often act through radical mechanisms this can lead to photoreduction to cyclopentanes, or photoaddition of the kind exemplified by norborneneand propan-2-ol 12.57). The photoadduct in this process is linked through the carbon atom of the alcohol, and not the oxygen atom. A related addition to acetonitrile 12.58) takes place when norbornene is irradiated in the presence of a silver(i) compound. It is likely thal a metal complex of the alkene is the real irradiation substrate, and the same may be true for copper(i)-promoted additions of haloalkanes to electron-deficient alkenes (2.59). When dichloromelhane is used in such a reaction the product can be reduced electrochemically to a cyclopropane (2.60), which is of value because the related thermal addition of CH.I, to alkenes in the presence of copper does not succeed with electron-poor compounds. 

Diene triplets can also be made to add to perhaloolefins,266 although with less ease than to ground-state dienes. Again the products are those expected from the most stable biradical intermediates, and the product ratios differ from those obtained in thermal additions. No photosensitized dimerization of the haloolefins occurs. 

Such [2 + 2] thermal additions generally are limited to polyhaloethenes and a few substances with cumulated double bonds, such as 1,2-propadiene (CH2=C=CH2) and ketenes (R2C=C=0). Some examples follow ... 

Padwa and Hamilton s work43 has been extended to the A-cyclohexyl derivatives (43, 45). With these compounds the thermal addition of... 

Thermal addition (105°-142°) of DMAD to other N-substituted pyrroles (19a-d)80 83 gave azabicycloheptadienes (20) in yields of 30-45% lower temperatures sufficed for 19e-h. The reversibility of the addition was demonstrated for 20f, 60% of which after 9 hours at 65° in carbon tetrachloride was converted back into 19f compound 20h, however, was unaffected. The azabicycloheptadiene 20 (R = C02Et) undergoes cycloaddition with 1 mole of 2,4,6-trimethylbenzonitrile oxide at both double bonds to give 26 and 27, and both these products... 

Thermal addition of DMAD to 4-halosydnones (85) gave 86, which was hydrolyzed to 87 and 88, halogen being retained.515... 

Thermal addition of DMAD to 3-(T-dimethylaminovinyl)indolizine (49 R = Me or Ph) in toluene gave cyclopenta[c]quinolizine (53) via a cyclobutene601 and the diene 51 (Scheme 18). Formation of 53 involves a rearrangement apparently without precedent. By carrying out the addition in methanol, the zwitterion was intercepted by proton transfer to give 50, which was converted into the isomeric quinolizine 52 in boiling xylene.600... 

Thermal additions might nevertheless in some instances follow the allowed 2s + 2a process. Figure 12.1 illustrates the approximate geometry required of a 2s + 2a transition state there will be serious hindrance to the approach by the groups R. In a search for this reaction, it will therefore be appropriate to have the groups R as small as possible. Bartlett and his collaborators have examined the stereochemistry of addition of tetrafluoroethylene to cis- and trans- 1,2-di-deuterioethylene 34 the results, summarized in Equation 12.16, demonstrate that the reaction is stepwise. Other experiments aimed at detecting the 2s + 2a process in olefins have similarly led to negative results.35... 

Thermal addition of SXC12 to fluoroolefins was often referred to as electrophilic addition [136, 137], although observed orientation of addition actually resembles that in radical reactions [139], Regardless of the mechanism, this reaction is highly regioselective and undoubtedly has synthetic value as a high yield route to polyfluoroalkyldisulfides. 

Shortly after Haszeldine s initial studies, Tarrant, Brace, and others began to use Kharasch s technique of diacyl peroxide initiation of such thermal additions [60, 216-227]. With such inducement, these addition processes could be run at lower temperature and usually with greater efficiency. Nevertheless, such radical-... 

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