Intramolecular Diels—Alder Reactions. III. Cyclizations of trans-Cinnamyl and Phenylpropargyl Phenylpropiolates^1a

The intramolecular Diels-Alder reaction

“…Thus, neither furfurylacetic acid derivatives 57a-c nor furfuryl alcohol derivatives 57d-f appear to cyclize,36,37 with the possible exception of furfuryl cinnamyl ether, which gives 2-methyl-3-phenylbenzaldehyde in high yield on flow pyrolysis at 400 °C,37 as in eq 7. A mechanism involving The cyclizations of a series of alkenylcyclohexadienes (63) has been reported. Structures have not yet been determined for the example where n = 4, however.423,15,43…”

“…A typical example would be the cyclization of cinnamyl propiolate as shown in eq 9. 63 In place of the benzene ring, thiophene has also been used; however, yields are rather modest. 64 The reaction is clearly capable of considerable extension.…”

Thermal Cycloisomerization of Putative Allenylpyridines for the Synthesis of Isoquinoline Derivatives

“…There are several reasons why the prospective isoquinoline synthesis shown in eq may exceed the limits of reactivity. Most significantly, to produce the postulated cycloaddition intermediate ( 1a ) would require introduction of a strained cyclic allene and disruption of pyridine aromaticity. , Secondary considerations include the unactivated alkyne dienophile and malonate ester functionality, which provides the desired Thorpe–Ingold conformational bias but may also introduce competing decomposition pathways.…”

Synthesis and Computational Studies Demonstrate the Utility of an Intramolecular Styryl Diels–Alder Reaction and Di-t-butylhydroxytoluene Assisted [1,3]-Shift to Construct Anticancer dl-Deoxypodophyllotoxin

“…The intramolecular styryl Diels–Alder (ISDA) reaction is a [4 + 2] cycloaddition that utilizes styryl functionality acting as the diene to react with electron deficient alkyne dienophiles . While this cycloaddition holds significant promise for the construction of complex structures, there are only limited examples of successful use.…”

“…With the successful coupling of pieces 4 and 6 , the original Klemm thermal conditions (DMF, reflux 190 °C) were initially examined for the key ISDA reaction of the electron-rich diaryl allyl propiolate ester 7 (Table ). Unfortunately, these conditions resulted in low yields (<10%) with extensive decomposition.…”