Synthons for the Parent Vinyl Carbene Complex in the Benzannulation Reaction
The benzannulation reaction of Fischer carbene complexes with alkynes to produce phenols was found not be synthetically useful for the parent vinyl carbene complex 6a.The β-silylated vinyl carbene complex 6c is more stable than the parent vinyl complex 6a and can be effectively used as a synthon for 6a since during the benzannulation the silicon migrates to the phenol function preferentially over hydrogen to give the arene chromium tricarbonyl complexes of the type 19.This reaction is general for a number of alkynes that have incorporated important functionality and is more useful for terminal alkynes than for internal alkynes.The migration of the silicon is responsible for the fact that stable arene chromium tricarbonyl complexes can be isolated from these reactions and makes possible transformations that take advantage of the activating ability of the chromium tricarbonyl group.This is demonstrated in intramolecular aromatic nucleophilic additions reactions.It is also shown in a single example that the α-silylated vinyl carbene complex 10b can in principle also serve as a synthon for the parent vinyl carbene complex 6a, since the benzannulated product can be disilylated with trifluoroacetic acid.
Total Synthesis of Pyrolaside B: Phenol Trimerization through Sequenced Oxidative C?C and C?O Coupling
A facile method to oxidatively trimerize phenols using a catalytic aerobic copper system is described. The mechanism of this transformation was probed, yielding insight that enabled cross-coupling trimerizations. With this method, the natural product pyro
Kozlowski, Marisa C.,Neuhaus, William C.
p. 7842 - 7847
(2020/04/03)
Alternative Lewis acids to effect Claisen rearrangement
Yb(OTf)3 and DIBAL-H are developed as alternative Lewis acids for effecting Claisen rearrangement of allyl, crotyl and prenyl aryl ethers.
Sharma,Ilangovan,Sreenivas, Punna,Mahalingam
p. 615 - 618
(2007/10/03)
Photochemistry of Substituted 4,4-Dimethoxy-2,5-Cyclohexadienones
4,4-Dimethoxy-2,5-cyclohexadienones 9-14 were prepared from the corresponding hydroquinone monomethyl ethers by oxidation with thallium trinitrate in methanol. Irradiation of solutions of 9-13 in methanol with a broad band of UV light centered at 350 nm in a Rayonet reactor afforded 2-cyclopentenone derivatives 15-19 in moderate to excellent yields, whereas irradiation of 14 in methanol gave phenol 8 along with other unidentified products. Irradiation of 11-14 in benzene yielded substituted phenols. The plausible reaction pathways for the product formation are discussed.