Cyclopropanation intramolecular-Cope rearrangement

The rhodium(ii)-catalyzed intramolecular reaction between linked vinyldiazomethanes and pyrroles leads to a novel synthesis of fused tropanes <1996JOC2305>. The reaction occurs by a stepwise [3- -4]-annulation mechanism between a rhodium-stabilized vinylcarbenoid intermediate and the pyrrole rather than by the typical tandem cyclopropanation/Cope rearrangement sequence. The outcome of the reaction is very sensitive to the vinylcarbenoid structure. In particular, the presence of a siloxy substituent on the vinylcarbenoid strongly favors the formation of fused tropanes 1063 or 1064 (Scheme 206) <1996JOC2305>. 

Dioxolanone 33 is obtained when the unsaturated silyldiazoester 30 is decomposed by Rh2(pfb)4 in the presence of an aldehyde or of acetone (Scheme 11) [21]. The reaction sequence is likely to include formation and (probably reversible) 1,5-cyclization of carbonyl ylide 31, and Cope rearrangement of the allylvinylether 32. In analogy to carbonyl ylide 21, the SiMe3 should occupy the exo-position in 31, thereby bringing the ester carbonyl in a geometry that is favorable to the cyclization step. Again, the choice of catalyst determines the product pattern, since CuOTf catalysis affords not only 33, but also oxirane 22 and the intramolecular cyclopropanation product 34. 

Vapor phase thermolysis of 2,5-hexadien-l-ols at 260°C affords cyclopropylmethyl ketones . The reaction has been proposed to proceed via homodienyl migration of hydrogen and is stereospecific (equation 118). l-(l-Alkynyl)-2-vinyloxiranes undergo successive Cope rearrangements at 300-350°C to give 2-(l-alkynyl)cyclopropane-carbaldehydes (equation 119) . Acid-catalyzed intramolecular acetalization followed by... 

The intramolecular reaction of the carbene from diazo ester 280, which contains a 1,3-diene moiety in the ester group and a double bond adjacent to the carbene center, leads to the formation of a substituted 1,2-divinyl-cyclopropane, whose CIS isomer then undergoes a Cope rearrangement to give substituted cycloheptadiene. In such a way, bicyclic 281 and tricyclic 282 y-lactones with a neighboring seven-membered carbocycle have been obtained (89JOC930). 

The Claisen rearrangement can be formally considered as an intramolecular SN2 addition of a carbonyl enol to an allylic alcohol. In contrast to the Cope rearrangement (see Section D.l. 6.3.1.2.), it is an irreversible, highly exothermic reaction with the exception of some special substrates, such as cyclopropane derivatives43,44 or some bicyclic compounds45-47. 

Tricyclic compounds result when in intramolecular cyclopropanation/Cope rearrangements the double bond of the diene moiety next to the tether is incorporated in a ring, e.g., formation of 122 and 124878. 

Reaction with benzene follows a similar pathway, yielding a bicyclo[3.2.2]nonatriene structure. Vinylcarbenoids also react with pyrroles to give tropanes via a cyclopropanation-Cope rearrangement route. The direct addition of carbenes to acetylenes does not give satisfactory yields of cyclopropanes, but the rhodium carboxylate catalysed reaction of diazo compounds with acetylenes is a useful source of cyclopro-panes. Carbenoids can also attack a carbonyl oxygen atom, giving rise to a zwitterion (249). An excellent review of intramolecular carbenoid reactions has appeared. ... 

Novel spirocyclic compounds have been prepared by the Cope rearrangement of taxane-like tricyclic compounds having a 1,5-diene moiety. The transformation was found to be reversible and the product distribution was found to be greatly dependent on the solvent polarity. The intramolecular cyclopropanation of dienylmethyl vinyldiazoacetate, followed by a Cope rearrangement, has been used in the... 

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