4.2.8. Reductive Coupling 3109 5. Reaction of Aromatic Compounds 3110 5.1. Electrophilic Substitutions 3110 5.2. Radical Substitution 3111 5.3. Oxidative Coupling 3111 5.4. Photochemical Reactions 3111 6. Reaction of Carbonyl Compounds 3111 6.1. Nucleophilic Additions 3111 6.1.1. Allylation 3111 6.1.2. Propargylation 3120 6.1.3. Benzylation 3121 6.1.4. Arylation/Vinylation 3121 6.1.5. Alkynylation 3121 6.1.6. Alkylation 3121 6.1.7. Reformatsky-Type Reaction 3122 6.1.8. Direct Aldol Reaction 3122 6.1.9. Mukaiyama Aldol Reaction 3124 6.1.10. Hydrogen Cyanide Addition 3125 6.2. Pinacol Coupling 3126 6.3. Wittig Reactions 3126 7. Reaction of R,â-Unsaturated Carbonyl Compounds 3127

Organic Reactions in Aqueous Media with a Focus on Carbon−Carbon Bond Formations: A Decade Update

Metal-catalyzed cycloisomerization reactions of 1,n-enynes have appeared as conceptually and chemically highly attractive processes as they contribute to the highly demanded search for atom economy and allow the discovery of new reactions. Since the pioneering studies with palladium by the research group of Barry Trost in the mid-1980s, several other metals have been identified as excellent catalysts for the rearrangement of enyne skeletons. Moreover, the behavior of 1,n-enynes may be influenced by other functional groups such as alcohols, aldehydes, ethers, alkenes, or alkynes, thus enhancing the molecular complexity of the synthesized products. Apart from the intrinsic rearrangements of 1,n-enynes, several tandem reactions incorporating intramolecular trapping agents or intermolecular partners have been discovered. This Review aims to highlight the main contributions in this field of catalysis and to propose and comment on the mechanistic insights of the recent discoveries.

Cycloisomerization of 1,n-enynes: challenging metal-catalyzed rearrangements and mechanistic insights.

3.1.2. From Vinylic Grignard Reagents 1437 3.1.3. From Aryl Halides and Alkenyl Acetates 1438 3.2. Aryl-Aryl Cross-coupling 1438 3.2.1. From Aromatic Organometallic Reagents 1438 3.2.2. From Two Aromatic Halides 1440 4. Csp2-Csp3 Cross-coupling Reactions 1440 4.1. Alkenylation 1440 4.1.1. From Aliphatic Organometallic Reagents 1440 4.1.2. From Aliphatic Halides 1442 4.2. Arylation 1442 4.2.1. From Aliphatic Halides 1442 4.2.2. From Aromatic Halides 1445 4.3. Allylation of Aromatic Organometallics 1446 5. Alkynylation 1446 5.1. Pioneering Works 1446 5.2. Benzylation of Acetylenic Grignard Reagents 1446 5.3. Alkylation of Acetylenic Grignard Reagents 1447 5.4. Alkenylation of Acetylenic Grignard Reagents 1447 6. Csp3-Csp3 Cross-coupling 1448 6.1. Allylation 1448 6.1.1. Allylation of Aliphatic Organozinc Compounds 1448

Cobalt-Catalyzed Cross-Coupling Reactions

The recent advent of transition-metal mediated CH activation is revolutionizing the synthetic field and gradually infusing a “CH activation mind-set” in both students and practitioners of organic synthesis. As a powerful testament of this emerging synthetic tool, applications of CH activation in the context of total synthesis of complex natural products are beginning to blossom. Herein, recently completed total syntheses showcasing creative and ingenious incorporation of CH activation as a strategic manoeuver are compared with their “non-CH activation” counterparts, illuminating a new paradigm in strategic synthetic design.

C-H activation: a complementary tool in the total synthesis of complex natural products.

http://web4.uwindsor.ca/users/j/jlichaa/reference.nsf/0/10ff8b04ff3a317885256d88005720f6/$FILE/tet-2000-56-3262-brummond.pdf

Recent Advances in the Pauson–Khand Reaction and Related [2+2+1] Cycloadditions

When the Pauson-Khand and Pauson-Khand type reactions go awry: a plethora of unexpected results

In this report we have shown that the commercially available Co(2)(CO)(8) and Co(4)(CO)(12), and enyne--Co(2)(CO)(6) complexes, are sufficiently effective in catalyzing the Pauson--Khand reaction under one atmosphere of CO pressure. It was further demonstrated that the efficiencies of these cyclization protocols could be enhanced by the presence of cyclohexylamine. These procedures have also rendered more practical and highly convenient alternatives for the catalytic Pauson--Khand reaction. Most importantly, we have dispelled the common belief that Co(4)(CO)(12) is inactive in the Pauson--Khand reaction under one atmosphere of carbon monoxide. Of mechanistic importance is that these studies have also shown that the probable formation of Co(4)(CO)(12) is not necessarily a dead end pathway in the Co(2)(CO)(8)-catalyzed Pauson--Khand reaction. It is also of interest that substoichiometric amounts of Co(2)(CO)(8), in DME and in the presence of cyclohexylamine, are sufficient for the cyclocarbonylation of enynes under a nitrogen atmosphere. Our findings have provided more practical protocols for the Pauson-Khand reaction using catalytic amounts of cobalt carbonyl complexes and a better understanding of the influence of Lewis bases on their efficiency. These reports on the activity of Co(4)(CO)(12) are anticipated to develop into a convenient and practical alternative for Co(2)(CO)(8) catalysis.

Practical cobalt carbonyl catalysis in the thermal Pauson--Khand reaction: efficiency enhancement using Lewis bases.

Depending on the thermolytic conditions, dicobalthexacarbonyl-complexed enynes underwent cyclizations to provide different carbocyclic frameworks. Bicyclopentanones were formed from enyne−Co2(CO)6 complexes, or from enynes that were treated with Co2(CO)8, or more effectively, with Co4(CO)12 in an alcoholic solvent under a H2 or N2 atmosphere. This transformation proceeded via a sequential cyclocarbonylation and 1,4-reduction and is the first account using the cobalt carbonyl cluster. Under these conditions a cobalt hydride was presumably generated, which mediated reduction of the enone to the saturated ketone. In contrast, thermolysis of dicobalthexacarbonyl-complexed enynes under a hydrogen atmosphere in toluene resulted in their reductive cyclization to form monocyclic alkenes in moderate yields, in addition to the bicyclopentenone product. In some cases, addition of a hydrosilane to the reaction induced a complete suppression of the bicyclopentenone formation. While the former results demonstrate a rea...

Llorente V. R. Bonaga

Papers

When the Pauson-Khand and Pauson-Khand type reactions go awry: a plethora of unexpected results

Practical cobalt carbonyl catalysis in the thermal Pauson--Khand reaction: efficiency enhancement using Lewis bases.

Cobalt carbonyl-mediated carbocyclizations of enynes: generation of bicyclooctanones or monocyclic alkenes.

Synthesis of medium-sized rings using the intramolecular Pauson–Khand reaction

Modification and limitations of the Livinghouse catalytic Pauson-Khand reaction