Iron-Catalyzed C(sp 3 )−C(sp 3 ) Bond Formation in 3,4-Dihydro-1,4-benzoxazin-2-ones

Stereoselective Cyclization Cascade of Dihydroquinoxalinones by Visible-Light Photocatalysis: Access to the Polycyclic Quinoxalin-2(1H)-ones

An intriguing stereoselective visible-light photocatalysis of dihydroquinoxalinone derivatives has been realized via cyclization with or without the solvolysis cascade. The reactions provided the polycyclic ring structures with efficient formation of multiple bonds and with high stereoselectivity. X-ray crystallography unequivocally determined the structures of five polycyclic products.

Ionic liquid-catalyzed synthesis of (1,4-benzoxazin-3-yl) malonate derivatives via cross-dehydrogenative-coupling reactions

A convenient C(sp3)–C(sp3) oxidative dehydrogenative coupling reaction of 1,4-benzoxazin-2-ones with malonate esters was developed under mild conditions to obtain the respective ester malonates in high yields. Reactions take place in [omim]FeCl4, acting as both the solvent and the catalyst. Under [omim]Cl/FeCl3-DDQ conditions, derivatives of 1 coupled with malonate 2 to give the target molecules within 1–2 h time periods. The ionic liquid was recovered and reused in the next reactions without losing its efficiency.

Peroxidation of 3,4-dihydro-1,4-benzoxazin-2-ones

The sp³-C-H peroxidation of 3,4-dihydro-1,4-benzoxazin-2-ones was achieved under mild and simple catalyst-free reaction conditions. A range of biologically important alkylated benzoxazinone peroxides are synthesized in high yield with a good functional group tolerance. The C(sp³)-OO bond was constructed efficiently and could be further converted into C(sp³)-C(sp³), C(sp³)-C(sp²), C(sp³)-C(sp), C-P and C[double bond, length as m-dash]O bonds by late-stage functional group transformations.

A walk around the application of nanocatalysts for cross-dehydrogenative coupling of C–H bonds

Cross-dehydrogenative coupling reactions between two unmodified C–H bonds are one of the most attractive and fundamental strategies for the construction of C–C bonds. As these reactions avoid pre-functionalization and de-functionalization of the substrates, they are cleaner, safer, and faster than traditional cross-coupling reactions. After the introduction of the modern area of cross-dehydrogenative coupling in 2003, many efforts have been devoted to the development of more efficient and selective catalytic systems for these appealing reactions. Among the different types of catalytic systems that have been investigated, nanostructured metal catalysts are highly attractive in view of their high catalytic performance, easy separability and good reusability. The purpose of this review is to focus on the application of nanocatalysts for cross-dehydrogenative coupling of C–H bonds with particular emphasis on the mechanistic aspects of the reactions. Specifically, we have structured this review based on the type of C–C bonds. Thus, the review is divided into six major sections: (i) C(sp³)–C(sp³) coupling; (ii) C(sp³)–C(sp²) coupling; (iii) C(sp³)–C(sp) coupling; (iv) C(sp²)–C(sp²) coupling; (v) C(sp²)–C(sp) coupling; and (vi) C(sp)–C(sp) coupling.

Cross-dehydrogenative coupling reactions between two unmodified C–H bonds are one of the most attractive and fundamental strategies for the construction of C–C bonds.

9,10-Phenanthrenedione as Visible-Light Photoredox Catalyst: A Green Methodology for the Functionalization of 3,4-Dihydro-1,4-Benzoxazin-2-Ones through a Friedel-Crafts Reaction

A visible-light photoredox functionalization of 3,4-dihydro-1,4-benzoxazin-2-ones through a Friedel-Crafts reaction with indoles using an inexpensive organophotoredox catalyst is described. The reaction uses a dual catalytic system that is formed by a photocatalyst simple and cheap, 9,10-phenanthrenedione, and a Lewis acid, Zn(OTf)2. 5W white LEDs are used as visible-light source and oxygen from air as a terminal oxidant, obtaining the corresponding products with good yields. The reaction can be extended to other electron-rich arenes. Our methodology represents one of the most valuable and sustainable approach for the functionalization of 3,4-dihydro-1,4-benzoxazin-2-ones, as compared to the reported procedures. Furthermore, several transformations were carried out, such as the synthesis of the natural product cephalandole A and a tryptophol derivative.

Visible-light-induced C(sp3)–H activation for a C–C bond forming reaction of 3,4-dihydroquinoxalin-2(1H)-one with nucleophiles using oxygen with a photoredox catalyst or under catalyst-free conditions

A convenient photocatalyzed oxidative coupling reaction of 4-alkyl-3,4-dihydroquinoxalin-2(1H)-one and its derivatives with a variety of nucleophiles was developed with a ruthenium photoredox catalyst and oxygen under a household compact fluorescent light. With a slower reaction rate, the cross coupling transformation can be achieved in the absence of an external photocatalyst with a similar isolated yield. An application to the synthesis of natural product cephalandole A was also demonstrated.

A convenient photocatalyzed coupling reaction of 4-alkyl-3,4-dihydroquinoxalin-2(1H)-one with a variety of nucleophiles was developed with a household compact fluorescent light. The synthesis of natural product cephalandole A was also demonstrated.

Copper-catalyzed oxidative phosphonation of 3,4-dihydro-1,4-benzoxazin-2-ones

A straight-forward and atom-economical Cu(ii)/PBQ-catalyzed oxidative Pudovik reaction of 3,4-dihydro-1,4-benzoxazin-2-ones has been developed to construct new C_sp3–P bonds.