COPE process

A mechanistic rationale for the observed cw-selectivity has been proposed based on preorganisation of the Breslow-type intermediate and imine through hydrogen bonding 253, with an aza-benzoin oxy-Cope process proposed. Reaction via a boat transition state delivers the observed cw-stereochemistry of the product (Scheme 12.57). Related work by Nair and co-workers (using enones 42 in place of a,P-unsaturated sulfonylimines 251, see Section 12.2.2) generates P-lactones 43 with fran -ring substituents, while the P-lactam products 252 possess a cw-stereo-chemical relationship. 

Shortly after this prediction, Schroder (1963) isolated bullvalene. Numerous studies amply demonstrated the facile Cope rearrangement of [84] and its derivatives (see for example Schroder and Oth, 1967 Doering et al., 1967). Theory and experiment agree that, by pinching the methano bridges closer together, the rate of the Cope process increases in the sequence semibullvalene [83] > barbaralane [85] > bullvalene [84] (Dewar and Schoeller, 1971 Anastassiou et al., 1975). 

When the conjugation is further extended, as in the triene-conjugated nitrile ylides (347), it is interesting that 1,1-cycloaddition still appears to be the favored primary process. In the case of the cis isomers 347 [R R =Me, Ph or (CH2)3 R = Ph, Me, C02Me] the proximate products (348) were not isolated but rearranged spontaneously via an aza-Cope process to give the bridged isoquinolines (349) in moderate yield (20-65%) (60,206). 

Psychological support can be very helpful (also see entry 181). Due to the enormous changes of life with MCS, you may feel overwhelmed. It s nice to have someone entirely outside of your daily life with whom to get things off your chest and to ask for guidance in the coping process. Losing touch with your friends and family can also be so emotionally intense as to demand psychological help. 

The enthalpy of activation is distinctively higher for the valence isomerization than for the Cope process. This clearly shows that the bicyclo is not an intermediate during the Cope rearrangement. The stereochemical process of the Cope rearrangement, in which the... 

Piers and Ruediger have smartly used this basic reaction (equation 168) for a synthesis of the sesquiterpenoid -himachalene ". However, loading the systems to be rearranged with alkyl groups can considerably decelerate the Cope process with the result of competing homo[l, 5]-sigmatropic hydrogen shift in the trans compounds (equation... 

The bicyclic cyclopropyl ketone shown in equation 174—easily accessible from the corresponding diazocarbonyl compound—could be transformed into two bicyclic divinylcyclopropanes with different functionality and positioning of the cyclopentene double bond. Rearrangement of these compounds leads to the bicyclo[12.1]octane series Very recent syntheses of the terpenes sinularene and quadrone include a pivotal Cope process of divinylcyclopropanes generated and rearranged in an analogous fashion (equation 175) . 

Among the hetero-Cope processes the Claisen rearrangement is the most known. It was discovered in 1912 6 first in a series of related [3,3]-sigmatropic isomerizations... 

A study of the photochemical Cope reaction of the hexadienes 40 has been carried out under photoinduced electron-transfer conditions. Evidence was gathered for the formation of a chair cyclohexane-1,4-radical cation 41 °. In snch systems, where the radical cation is formed using DCA as the sensitizer, a degenerate Cope process is operative. Thus when the tetradeuterio derivative 42 is used, rearrangement affords a (52 48) mixture of the two dienes 42 and 43. Related to this general problem, DCA-sensitized reactions of the isomeric dienes 44 and , -45 and the cyclization prodnct, the bicyclohexane 46, have been studied in considerable detail. At low conversions, the irradiation of 46 affords a mixture of the dienes 44 and , -45 in ratios that are independent of temperature. The influence of the position of the aiyl groups on the diene skeleton has also been studied. This does not appear to affect the conversion to a cyclic radical cation. Thus the SET-induced reaction of the diene 47 has shown that the open chain radical cation of the diene 48 cyclizes preferentially to the radical cation 49. ... 

A high degree of chiral transmission is observed in the synthesis of iodo acetal 19, a key intermediate in the total synthesis of ( + )-faranal (a trail pheromone of the Pharaoh s ant). The [2,3] Wittig process ot 16 followed by cis hydrogenation gives oxy-Cope substrate 17 with 100% E and Z and >99% threo. The oxy-Cope process of 17 affords en7//ro-aldehyde 18 as a single product with 91 % ee966. 

From these results a stepwise mechanism has been deduced for the [1,3] rearrangement via fragmentation-recombination, with an intramolecular Michael addition of a cyclohexenyl anion to a conjugated cyclopentenyl moiety in the second stage1182. The exclusive formation of the regiomer 16 in both anionic oxy-Cope processes of 15a and 15b is probably due to nonbonded strain in the alternative intermediate 30 b. 

The Claisen rearrangement, a heteroatomic variant of the Cope process, holds equal appeal as a scaffolding element that is totally atom-efficient. We have addressed and defined those stereocontrol elements associated with a two-carbon intercalation tactic [55] in several contexts as, for example, in the preparation of (-f)-ceroplastol I (101) [56]. 

The enones (68) can be induced to cyclize to (69) using Pyrex-filtered light when BF3-Et20 is added to the system.39 An attractive mechanistic rationalization would involve a Cope process but this was excluded by the failure of the enol ether (70) to cyclize. This system undergoes cis-trans-isomerization, which is an efficient method of excited-state relaxation in these systems since the enone... 

A study of the photochemical behaviour of the diene (114) using DCA as the sensitizer has shown that a degenerate Cope process is operative. This treatment affords a mixture (52 48) of the two dienes (114) and (115), and a detailed study of this reaction has been carried out. 1,1-Diphenylhepta-1,6-diene (116) undergoes photocyclization to give the radical cation (117) which cyclizes via the six-membered transition state shown in (118). This intermediate is trapped by attack of acetonitrile to yield ultimately the adduct (119) which is formed in... 

Lazarus, R. S. (1966). Psychological Stress and the Coping Process. New York McGraw-Hill. 

Lazarus, R. S. (1977). Cognitive and coping processes in emotion. In A. Monat and R. S. Lazarus (eds) Stress and Coping An Anthology. New York Columbia University Press. 

Subjective state Physical symptoms Evaluation of settings Actions, goals, coping process Comments on tasks, performance... 

Lundbetg, U. (1984). Human psychobiology in Scandinavia II. Psychoneuroendocrinology—human stress and coping processes. Scandinavian Journal of Psychology, 25, 214-226. 

The K-alkoxide of the startg. m. prepared with KH in anhydrous tetrahydrofuran heated several min. at 66° product. Y 98%. - Both the increased yield and lower reaction temp, in this anionic oxy-Cope process should improve the synthetic utility of these and related rearrangements. F. e. s. D. A. Evans and A. M. Golob, Am. Soc. 97, 4765 (1975). 

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