A

4-Acetamido-2,2,6,6-tetramethyl-1-oxopiperidinium tetrafluoroborate

Oxidation.

Hexafluoroisopropyl ester of aroic acids are generated by oxidation of mixtures of ArCHO and (CF3)2CHOH.1 Probably the hemiacetals are the critical substrates. As for acquiring aldehydes from oxidation of primary alcohols, the base must be carefully selected. Thus, in the case of 2-alkoxyethanols, 2,6-lutidine should be used.2

Alkyl perfluoroalkyl ketones undergo dehydrogenation on treatment with the oxopiperidinium salt and 2,6-collidine to furnish alkenyl perfluoroalkyl ketones.3

1. 1 Kelly, C.B., Mercadante, M.A., Wiles, R.J., Leadbeater, N.E. OL 15, 2222 (2013)
2. 2 Bobbitt, J.M., Bartelson, A.L., Bailey, W.F., Hamlin, T.A., Kelly, C.B. JOC 79, 1055 (2014)
3. 3 Hamlin, T.A., Kelly, C.B., Leadbeater, N.E. EJOC 3658 (2013)

Acetylacetonato(dicarbonyl)rhodium(I)

Addition.

The Rh(I) complex is the most reliable catalyst for hydroformylation, and research in the area concerns chiefly with ligands to modify its activity and robustness, although catalysts based on other metals such as Ru, Ir, Pd, and Fe have shown activities.1 Libraries of bisdiazophospholanes have been compiled regarding optimization of conditions for hydroformylation with the Rh chelate.2

Linear hydroformylation of functionalized alkenes at room temperature is benefited by 6-diphenylphosphino-2-pyridone as ligand.3 Alkenenitriles with an internal double bond and no obstruction to its isomerization toward the far terminus would undergo hydroformylation. The bond migration step is rate-determining.4 When the reaction is carried out in the presence of (acac)Rh(CO)2, Ru complex 1 and ligand 2, internal alkenes produce primary alcohols, as hydrogenation occurs succeeding hydroformylation.5

Control for production of linear vs branched aldehydes is of great interest. The dibenzophosphole ligand 3 favors formation of the branched aldehyde from styrene to the extent of 95:5.6 A more elaborate ligand construct is to coordinate each of the three nitrogen atoms of tri(3-pyridyl)phosphine to tetraphenylporphyrinatozinc(II). On exchange of the huge ligand with one CO on the rhodium center a catalyst that favors branched hydroformylation is created.7 The ligand 4 has a pocket for binding and preorganization in close proximity to the metal-coordination site, with it the reaction occurs predominantly in a way contrary to the usual trend.8 Ligand 5 for the Rh complex favors linear hydroformylation.9

A method for catalyst recycling after hydroformylation of long-chain alkenes involves temperature manipulation.10 A multicomponent solvent system consisting of PEG-400, dioxane, and n-heptane is crucial. The reaction is made heterogeneous afterward by cooling for facile recovery of the catalyst and ligand (Biphephos).

2-Alkenoic acids are converted to saturated primary alcohols of the same carbon chain length by a process that involves decarboxylation, hydroformylation and hydrogenation.11

Addition.

Exposure of 1-alken-3-ones and 1-alkynes to (acac)Rh(CO)2 and (o-Tol)3P in toluene at 80° leads to adducts containing a saturated ketone and a conjugated enyne unit.12 The reaction proceeds via dimerization of the alkynes before the conjugate addition.

Cyclization.

o-Aryloxybenzoic acids form dibenzofurans with loss of the carboxyl group and two hydrogen atoms on heating with (acac)Rh(cod), an analog of (acac)Rh(CO)2, in Ac2O containing KI.13 o-(Methoxycarbonylamino)cinnamyl alcohols and analogs undergoes hydroformylation at the benzylic position which is amenable to a short synthesis ot desoxyeseroline.14

1. 1 Pospech, J., Fleischer, I., Franks, R., Buchholz, S., Beller, M. ACIE 52, 2852 (2013)
2. 2 Adint, T.T., Wong, G.W., Landis, C.R. JOC 78, 4231 (2013)
3. 3 Straub, A.T., Otto, M., Usui, I., Breit, B. ASC 355, 2071 (2013)
4. 4 Ternel, J., Couturier, J.-L., Dubois, J.-L., Carpentier, J.-F. ASC 355, 3191 (2013)
5. 5 Yuki, Y., Takahashi, K., Tanaka, Y., Nozaki, K. JACS 135, 17393 (2013)
6. 6 Oukhrib, A., Bonnafoux, B., Panossian, A., Waifang, S., Nguyen, D.H., Urrutigoity, M., Colobert, F., Gouygou, M., Leroux, F.R. T 70, 1431 (2014)
7. 7 Besset, T., Norman, D.W., Reek, J.N.H. ASC 355, 348 (2013)
8. 8 Dydio, P., Reek, J.N.H. ACIE 52, 3878 (2013); X Dydio, P., Detz, R.J., de Bruin, B., Reek, J.N.H. JACS 136, 8418 (2014)
9. 9 Chen, C., Qiao, Y., Geng, H., Zhang, X. OL 15, 1048 (2013)
10. 10 Brunsch, Y., Behr, A. ACIE 52, 1586 (2013)
11. 11 Diab, L., Gellrich, U., Breit, B. CC 49, 9737 (2013)
12. 12 Lerum, R.V., Russo, C.M., Marquez, J.E., Chisholm, J.D. ASC 355, 3485 (2013)
13. 13 Maetani, S., Fukuyama, T., Ryu, I. OL 15, 2754 (2013)
14. 14 Chiou, W.-H., Kao, C.-L., Tsai, J.-C., Chang, Y.-M. CC 49, 8232 (2013)

Alkynyl(o-methoxyphenyl)iodonium salts

Alkynyl group transfer.

In comparison with those with an unsubstituted phenyl group the methoxy substituent improves reactivity of the reagents.1

1. 1 Hamnett, D.J., Moran, W.J. OBC 12, 4156 (2014)

?3-Allyl(cyclopentadienyl)palladium

Substitution.

Cinnamyloxy derivatives with a ß-fluoro substituent undergo double substitution by malonic esters.1 The Pd complex is able to activate the alkenyl fluorine.

Addition.

A metathetic cyclization involving an N-cyanoanilide unit and a double bond of an o-methallyl side chain generates 2-cyanomethylindoline derivatives.2

An access to 3-arylidenepyrrolidines by syn-addition of the aryl group from ArB(OH)2 and the iminium species derived from a homopropargylamine and formaldehyde is promoted by CpPd(?3-C3H5).3

Cyclic shuffle.

A remarkable transformation mediated by CpPd(?3-C3H5) is the breaking of the 3-[o-(1-silacyclobutyl)phenyl]cyclobutanone system to create benzosiloles.4

1. 1 Yamamoto, M., Hayashi, S., Isa, K., Kawatsura, M. OL 16, 700 (2014)
2. 2 Miyazaki, Y., Ohta, N., Semba, K., Nakao, Y. JACS 136, 3732 (2014)
3. 3 Tsukamoto, H., Shiraishi, M., Doi, T. OL 15, 5932 (2013)
4. 4 Ishida, N., Ikemoto, W., Murakami, M. JACS 136, 5912 (2014)

Aluminum bromide

Substitution.

Hydride abstraction from C-1 of adamantane on grinding with AlBr3 and CBr4 occurs; when an amine is also present the bridgedhead cation is trapped to produce the 1-aminoadamantane.1

1. 1 Wei, Z., Li, J., Wang, N., Zhang, Q., Shi, D., Sun, K. T 70, 1395 (2014)

Aluminum chloride

Isomerization.

2-Aroylcyclopropane-1,1-dicarboxylic esters are subject to ring-opening isomerization by action of Lewis acids. Interestingly, different types of product are obtained from treatment with AlCl3, and TiCl4.1

Substitution.

Deoxygenative arylation of phloroglucinol is a convenient method for synthesis of 5-arylresorcinols.2 It is thought that all three oxygen atoms are coordinated to AlCl3 to expose a highly electrophilic cyclohexadienone for bonding with arenes.

The conclusion of a mersicarpine synthesis3 involves an intramolecular alkylation and imination.3

The reaction of 1,1'-bicyclohexyl with acetyl chloride in the presence of AlCl3 is fascinating, as C-H acetylation occurs in one ring and oxygen atom insertion to a C-H bond of the other ring are involved.4

Electrophilic attack by aroyldithioacetic esters on phenols results in the formation of 4-aryl-2H-chromene-2-thiones.5

Cycloaddition.

Role reversal for nucleophile and electrophile is witnessed in the reaction of benzoquinone with acylketene dithioacetals.6 Still, AlCl3 is the essential mediator.

Ionization of a benzylic tosylamino group induced by AlCl3 in the presence of cyclopropane-1,1-dicarboxylic esters triggers indan formation.7

O-C bond cleavage.

Catechols protected as benzodioxepanes are recovered by heating with AlCl3 in benzene.8

1. 1 Sathishkannam, G., Srinivasan, K. ASC 356, 729 (2014)
2. 2 Gulyas-Fekete, G., Boluda, C.J., Westermann, B., Wessjohann, L.A. S 45, 3038 (2013)
3. 3 Lv, Z., Li, Z., Liang, G. OL 16, 1653...