Regio- and stereoselective addition of Brønsted acids to yndiamides: Synthesis of N,O,N- and N,S,N-trisubstituted ketene acetals

Yndiamides, N,N-disubstituted alkynes, are versatile building blocks for the synthesis of nitrogen-containing organic molecules. Unlike ynamides, relatives that are inherently polarized by a single nitrogen substituent, their pseudo-symmetric nature renders regioselective reactions challenging. Here we report investigations into the regioselective addition of Brønsted acids to non-symmetric yndiamides, a reaction that delivers N,O,N- and N,S,N-trisubstituted ketene acetals with excellent regio- and stereoselectivity.

Ruthenium Metal: Uplifting Regioselective C-H activation

: Construction of the C-C bond has always been a challenge for organic chemists, because of the reactivity of carbon atoms. The making of nucleophilic carbon started with the Grignard reagent, enolate, and the ylide, moreover, the aromatic carbon activation was the challenge before the era of organometallic chemistry. The recognition of organometallic chemistry was in the light when the Nobel Prize was given for the C-C bond in the year 2010, However, The pre functionalization of the C-H bond was an additional step with halogenated reagent, which was the limitation of this reaction. Later the C-H activation with organometals like Pd, Ru, Cu, Rh, and other transition metal came into existence, where the directing group and metal makes feasibility to form the nonreactive C-C bond. In spite of several organometals, Ru made a special place due to the reactivity, coast and, stability. Various C-H activation reaction protocols were reported with their high regioselectivity as well as high atom economy. The C-H activation protocol is now in the next level of development like SP3, SP2 ortho, meta, and para C-H activation. Here in our aim is to get the summarized information regarding the Ru and their ortho -regioselective reactions with the help of the directing group. The reader will be benefited from the mechanistic part and the concept of C-H activation with some of the important examples, which have been summarized here in with the various Ru based regioselective reactions through weak and strong coordination of metal and substrate.

Silylboranes as Powerful Tools in Organic Synthesis: Stereo- and Regioselective Reactions with 1,n-Enynes

Bismetalated alkenes, accessible by element–element addition to alkynes, are valuable building blocks in organic synthesis, providing wide opportunities for divergent synthesis. Silaboration of alkynes with a pendant olefinic group, catalyzed by group 10 metal complexes, and subsequent transformation of the silicon and boron functional groups give access to densely functionalized 1,3-dienes and 1,3,5-trienes with defined stereo- and regiochemistry, 1,2-dienes, and carbocyclic and heterocyclic products.1 Introduction2 Background3 Reactions with 1,3-Enynes4 Cyclization 1,6-Enynes5 Cyclization 1,7-Enynes6 Cyclization of 1,n-Enynes (n > 7)7 Cyclization of Dienynes and Enediynes8 Cyclization of 1,6-Diynes9 Conclusions

Procedure-Economical, Enantioselective Total Syntheses of Polycyclic Natural Products and Analogues Containing a 3a-Hydroxyhexahydropyrrolo[2,3-b]indole-2-carboxylic Acid Residue

The 3a-hydroxyhexahydropyrrolo[2,3-b]indole-2-carboxylic acid (HPIC) residue and its aza-analogue are found in many bioactive natural products. In this account, short divergent total syntheses of several such natural products, diastereomers and analogues are described. It is demonstrated that by appropriate combination of different efficient tactics such as biomimetic/bio-inspired synthesis, chemo/regioselective reactions, umpolung of regioselectivity and/or reactivity, and tandem reactions, the enantioselective syntheses of polycyclic molecules such as (+)-asperlicin E and (–)-robustanoids A and B can be achieved in a protecting-group-free and redox-economical manner, in only three to four steps starting from l-tryptophan.1 Introduction2 Strategic Considerations2.1 Occurrence of HO-HPIC and HO-aza-HPIC Residues in Natural Products2.2 Biosyntheses of HO-HPIC and HO-aza-HPIC Residues2.3 Chemical Syntheses of HO-HPIC and HO-aza-HPIC Residues3 Procedure-Economical Syntheses of HO-HPIC-Containing Natural Products3.1 Protecting-Group-Free Syntheses of Asperlicin E, Its Diastereomer, and an Analogue3.2 Divergent Syntheses of (–)-Robustanoids A and B, a Diastereomer, and Analogues4 Conclusion and Future Perspectives

Chemo- and regioselective reactions of 5-bromo enones/enaminones with pyrazoles

The reaction of pyrazoles with 5-bromo enones furnished an unexpected series of stableN,O-aminals in a chemo- and regioselective and metal free reaction.