Shaibal Banerjee

Recent developments in the retro-Diels–Alder reaction

The retro-Diels–Alder reaction (rDA) has become an important tool for synthetic chemists in their quest towards the synthesis and design of novel scaffolds. The ability to carry out the rDA reaction under ambient conditions has made it quite attractive. In recent years the scope of the rDA in several areas has increased manifold. The present review covers the developments in this ever-expanding field over the last decade. The review will summarize various aspects of the rDA reaction and its applications to natural and non-natural products.

Retro Diels–Alder reaction under mild conditions: experimental and theoretical studies

We describe experimental as well as theoretical results to support the role of cyclopropane in a retro Diels-Alder reaction at lower temperature.

Pd-catalyzed regioselective arylation on the C-5 position of N-aryl 1,2,3-triazoles.

We herein report a highly efficient method for the arylation at the C-5 position of N-aryl 1,2,3-triazoles via a direct palladium catalyzed arylation reaction. The optimal reaction conditions required a combination of Pd(OAc)2 and tris(o-tolyl)phosphine as catalyst, and Cs2CO3 as the base under inert atmosphere. A variety of C-5 substituted N-aryl 1,2,3-triazoles were prepared using these conditions with yields in the 70-88% range. Regioselective C-5 arylations were also performed on 1,4-disubstituted 1,2,3-triazoles. The regioselectivity in triazole substitution at the C-5 position was confirmed by single crystal XRD. In addition, computational investigations of key steps of the catalytic cycle using the density functional theory have provided a rationalization to the selective C-5 arylation of N-aryl 1,2,3-triazoles.

Recent applications of ring-rearrangement metathesis in organic synthesis

Summary Ring-rearrangement metathesis (RRM) involves multiple metathesis processes such as ring-opening metathesis (ROM)/ring-closing metathesis (RCM) in a one-pot operation to generate complex targets. RRM delivers complex frameworks that are difficult to assemble by conventional methods. The noteworthy point about this type of protocol is multi-bond formation and it is an atom economic process. In this review, we have covered literature that appeared during the last seven years (2008–2014).

Synthesis of rare-earth doped ZnO nanorods and their defect–dopant correlated enhanced visible-orange luminescence

We report the synthesis of size controlled ZnO and rare-earth doped ZnO nanorods in the sub-10 nm diameter regime. The preferential anisotropic growth of the nanostructures along the polar c-axis leads to the formation of wurtzite phase ZnO nanorods. Photoluminescence measurements reveal enhancement of visible luminescence intensity with increasing RE3+ concentrations upon excitation of host ZnO into the band gap. The broad visible luminescence originates from multiple intrinsic or extrinsic defects. The luminescence from RE3+ is enabled by energy transfer from defect centers of the host nanocrystal lattice to dopant sites. Host–guest energy transfer facilitates efficient intra-4f orbital transitions (5D4 → 7Fj for Tb3+ and 5D0 → 7Fj for Eu3+) related characteristic green or red emission. Interestingly, different decay rates of host defects and RE3+ emission transition also allow temporal control to achieve either pure green or red color. This study suggests that manipulation of defects through bottom-up techniques is a viable method to modulate the energy transfer dynamics, which may help enable the future applications of ZnO-based phosphor materials in optoelectronic and multicolor emission displays.

Diversity oriented approach to polycyclics via cross-enyne metathesis and Diels–Alder reaction as key steps

AbstractPolycyclics containing biaryls have been prepared via application of cross-enyne metathesis and the Diels −Alder reaction. Here, ethylene and 1,5-hexadiene were used as a cross-coupling partners to generate key diene intermediates. Graphical AbstractPolycyclics containing biaryls have been prepared via application of cross-enyne metathesis and the Diels-Alder reaction. Here, ethylene and 1,5- hexadiene were used as a cross-coupling partners to generate key diene intermediates.

Correlation between carbon–carbon bond length and the ease of retro Diels–Alder reaction

AbstractThe bond length between C8-C9 in (1′R,4′S,4a′R,8a′S)-6′,7′-dimethyl-1′,4′,4a′,8a′-tetrahydrospiro [cyclopropane-1,9′-[1,4]methanonaphthalene]-5′,8′-dione is 1.571 (2) Å and between C7-C12 is 1.567 (2) Å which are longer than the corresponding bond length for saturated bicyclic systems (1.531-1.535 Å). This paper reports the correlation between bond length and the ease of retro Diels −Alder reaction. Graphical AbstractWe examined the crystal structure of (1′R,4′S,4a′R,8a′S)-6′,7′-dimethyl-1′,4′,4a′,8a′-tetrahydrospiro[cyclopropane-1,9′-[1,4] methano- naphthalene]-5′,8′-dione and found that the bond length between atoms connecting diene and the dienophile is somewhat longer than the normal C–C bond length. The increased bond length is responsible for the facile rDA reaction of 5.