Carbon-Heteroatom Bond-Forming or Cleaving Reactions

Carbon-Heteroatom Bond-Forming or Cleaving Reactions 891... 

The two a-bonds that are cleaved in the retro Diels-Alder reaction need not necessarily be the same as those formed in the initial forward reaction. Many valuable retro Diels-Alder reactions involve the cleavage of one carbon-carbon and one carbon-heteroatom bond, or two carbon-heteroatom bonds, that were not set up in a forward Diels-Alder reaction. For example, the otherwise relatively inaccessible 3-substituted and 3,4-disubstituted furans can be prepared by way of a tandem Diels-Alder then retro Diels-Alder reaction of 4-phenyloxazole and substituted alkynes, as illustrated in Scheme 3.87. 

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