intramolecular

Examples of intramolecular in the following topics:

• Cyclization by Intramolecular Addition Reactions

  • If a radical is joined to a double bond by a chain of three or more carbons intramolecular addition generates a ring.

• Ene Reactions

  • This is the same bond bookkeeping change exhibited by electrocyclic reactions, but no rings are formed or broken in an ene reaction unless it is intramolecular.
  • The following examples illustrate some typical ene reactions, with equation 3 being an intramolecular ene reaction.
  • This is the case for reactions 1 and 2, which proceed under milder conditions than 3, despite the latter's intramolecular nature.
  • Because this is an intramolecular ene reaction a new ring is formed.

• Reactions of Alkylidene Complexes

  • Equation # 5 shows a sequence involving epoxide alkylation, followed by an intramolecular trans-esterification analog.

• The Payne Rearrangement

  • Epoxy alcohols undergo reversible intramolecular epoxide opening reactions known as the Payne rearrangement.

• Multistep Transformations

  • The resulting diketone, in its cis-fused configuration, then undergoes an intramolecular Michael reaction, forming a new five-membered ring (note the colored bond).

• Cascade Reaction Sequences

  • In many cases carbon-carbon bond construction has been enhanced by sequences of intramolecular events termed tandem, domino or cascade reactions.
  • The second example shows an intramolecular hetero Diels-Alder cycloaddition, followed by bonding of the resulting immonium cation to a pendant tri-substituted double bond (an aza-Prins reaction).
  • The first example above is an interesting case of an acid catalyzed cascade of intramolecular epoxide openings, involving oxygen nucleophiles.
  • In this case the resulting allenic system is part of a conjugated diene, and undergoes an intramolecular Diels-Alder cycloaddition.

• Irreversible Substitution Reactions

  • The last example (reaction #4) is an interesting case of intramolecular alkylation of an enolate anion.
  • It is the rapid intramolecular nature of the alkylation that allows these unfavorable conditions to be used.
  • Although conformer II of the enolate anion could generate a stable five-membered ring by an intramolecular SN2 reaction, assuming proper orientation of the α and γ' carbon atoms, the concentration of this ideally coiled structure will be very low.
  • Ring closures to four, five, six and seven-membered are also possible by intramolecular enolate alkylation, as illustrated by the following example.

• Three-Membered Rings

  • Many examples of intramolecular interactions, such as example 10, have been documented.
  • An interesting regioselectivity in the intramolecular ring-opening reactions of disubstituted epoxides having a pendant γ-hydroxy substituent has been noted.

• Rearrangements of Cationic Oxygen

  • Once the peracid has added to the carbonyl group, the rearrangement may be facilitated by an intramolecular hydrogen bond, in the manner depicted in brackets on the right.
  • Peracid exchange with peracetic acid leads to an intramolecular Baeyer-Villiger reaction by way of the bicyclic acylperoxide drawn in brackets.

• Carbonyl Compounds

  • The second illustrates the intramolecular variant.
  • Three intramolecular type I reactions, all proceeding by way of biradical intermediates, demonstrate the variety of products that may be formed by hydrogen transfer disproportionation and/or ring closure.
  • The cyclic transition states for such intramolecular hydrogen transfer usually include five or six, and occasionally seven atoms.
  • These reactions all begin by an intramolecular hydrogen atom abstraction, similar to the intermolecular abstraction in the reductive dimerization of benzophenone.
  • In hydrocarbon solvents intramolecular hydrogen transfer back to carbon is common, reducing the quantum yield of these products by over 50%.