Ketene dithioacetals are versatile intermediates in organic synthesis. Extensive research, since the last decade, has given rise to new prospects in their chemistry. The objective of this review is twofold: first, to highlight the new prospects in the chemistry of functionalized ketene dithioacetals, and second, to provide an intrinsic link between ketene dithioacetal groups and a variety of other functional groups, which has brought out many new facts that will assist in future designs.

A new strategy, the 1,3-carbothiolation/aromatization, for the synthesis of functionalized (trifluoromethyl)arenes has been developed that enables the regioselective introduction of two different functional groups onto an "aromatic ring" in the meta-position to each other in a single step.

α-Acidic isocyanides are versatile reagents in organic synthesis, especially for the synthesis of five-membered heterocycles via [3 + 2]-cycloaddition reactions with activated multiple bonds. In this communication, the first [3 + 3]-cross-cycloaddition of α-acidic isocyanides with 1,3-dipolar azomethine imines to generate a series of 1,2,4-triazine derivatives with significant regiochemical control under mild catalytic reaction conditions is described. This new strategy shows that α-acidic isocyanides can also be taken as potent reagents for the synthesis of six-membered heterocycles through [3 + 3]-cross-cycloaddition reactions with 1,3-dipoles.

The indolizidine skeleton is one of the most important structural motifs found in numerous biologically active molecules. [1][2][3][4] The development of efficient methods for the synthesis of indolizidine alkaloids has been the subject of intense research. [1][2][3][4] Recently, we have been devoted to the research of heterocyclizations using alkenoyl ketene dithioacetals as five-carbon 1,5-dielectrophiles [5,6] and ethyl isocyanoacetate as both a double Michael donor and a 1,3-dipole in a [5C+1C] annulation process for the construction of complex heterocyclic systems (Scheme 1). [6] As part of our studies in this area, we herein report a new synthetic strategy for the construction of the tricyclic indolizidine alkaloids 3 by an unprecedented [7C+1C] annulation to deliver the 8azabicyclo[5.2.1]dec-8-enes 2 from the easily available dialkenoyl ketene dithioacetals 1 as C 7 1,7-dielectrophiles (Scheme 1). [5][6][7][8] Initially, the reaction of the dialkenoyl ketene dithioacetal 1 a with ethyl isocyanoacetate was investigated to evaluate a tandem process involving a [7C+1C] annulation with 1 a as a C 7 1,7-dielectrophile (Table 1). It was found that treatment of the mixture of 1 a (1.0 mmol) and ethyl isocyanoacetate (1.1 equiv) with NaOH (1.0 equiv) in THF at room temperature for 0.5 hours gave the fused oxazoline 4 a [8a] in 71 % yield and 8-azabicyclo[5.2.1]dec-8-ene 2 a in 17 % yield (entry 1). According to our previous reports, [5a,b, 6] the formation of 2 a would involve a [7C+1C] annulation process.Although synthetic approaches to five-and six-membered carbocycles are legion, encompassing both cyclization and cycloaddition approaches, the synthesis of medium-sized carbocycles from acyclic precursors is quite challenging because of unfavorable entropic and enthalpic factors which preclude ring formation. [9] For the construction of eightmembered carbocycles, transition-metal-catalyzed/mediated higher-order cycloadditions involving [2+2+2+2], [4+4], [4+2+2], [5+2+1], and [6+2] [9a] ring-closing metathesis, [9b] and related intramolecular reactions have been reported. [9,10]

Cobalamins (B12) play various important roles in vivo. Most B12-dependent enzymes are divided into three main subfamilies: adenosylcobalamin-dependent isomerases, methylcobalamin-dependent methyltransferases, and dehalogenases. Mimicking these B12 enzyme functions under non-enzymatic conditions offers good understanding of their elaborate reaction mechanisms. Furthermore, bio-inspiration offers a new approach to catalytic design for green and eco-friendly molecular transformations. As part of a study based on vitamin B12 derivatives including heptamethyl cobyrinate perchlorate, we describe biomimetic and bioinspired catalytic reactions with B12 enzyme functions. The reactions are classified according to the corresponding three B12 enzyme subfamilies, with a focus on our recent development on electrochemical and photochemical catalytic systems. Other important reactions are also described, with a focus on radical-involved reactions in terms of organic synthesis.