摘要：The chemistry of biradicals generated from thermal rearrangements discussed in this review is a rich area for discovery of new and unusual reactions. Clearly, the development of this field is still in its infancy and many discoveries still he ahead. The use of these biradicals for the synthesis of complex natural products is virtually unexplored. While interesting examples employing Bergman cyclization for the preparation of polyphenylenes, polynaphtha-lenes, and oligo(acenes) have been reported, applications of the biradical-forming reactions to materials synthesis have yet to be systematically investigated. Moreover, the feasibility of generating persistent radicals by these thermal processes has barely been demonstrated. Designing suitable systems as precursors to tetraradicals, hexaradicals, and potentially high-spin polyradicals remains an area for one to imagine.
摘要：The simple hydrocarbon called trimethylenemethane (TMM, 1) has been of interest to theoreticians and experimentalists for many years. Simple Hueckel molecular orbital calculations indicate the presence of a degenerate pair of non-bonding molecular orbit-als, Ψ_2 and Ψ_3, with the shape illustrated below. Clearly, singlet and triplet electronic configurations are possible, and as we shall see, the corresponding singlet and triplet states play a significant role in the chemistry of TMM derivatives.
摘要：It should be clear from this review that great strides have been made in developing the asymmetric potential of palladium-catalyzed allylic alkylations. Many reactions have been developed which rival the enantioselectivities of other commonly used transition metal-catalyzed reactions. The stereodynamic processes involved in the catalytic cycle provide different mechanisms for enantioselection. Each of these has been utilized, with varying degrees of success. As other transition metals are recruited for asymmetric allylic alkylations, complementary patterns of substrate tolerance may emerge. In this way, even the least cooperative substrates (unsym-metrically substituted racemic allylic substrates) may eventually yield to the continued efforts to develop these processes for use in enantioselective organic synthesis.
摘要：Synthetic organic chemistry has developed in a fascinating way over the past decades. Several highly selective procedures have been developed which allow the preparation of complex molecules with excellent regio-, chemo-, diastereo-, and enan-tioselectivity. One of the most remarkable examples is the synthesis of palytoxin with 64 stereogenic centers, from which over 10~(19) different stereoisomers could exist. Despite this great success and the importance of chemistry to our society its public image has deteriorated. This can be explained by the increasing importance of environmental issues to our society and the fear that chemistry could negatively influence the ecological balance. Today it is not only a question of what we can synthesize, but how we do it. Major problems in chemical production are the handling of waste, the search for environmental tolerable procedures, the preservation of resources, and the increase in efficiency. The solution of these problems would not only be favorable for the environment, but also allow a reduction in production cost.
摘要：Tandem ylide generation from the reaction of metallo carbenoids with heteroatoms continues to be of great interest both mechanistically and synthetically. Effective ylide formation in transition metal-catalyzed reactions of diazo compounds depends on the catalyst, the diazo species, the nature of the heteroatom, and competition with other processes. The many structurally diverse and highly successful examples cited in this review clearly indicate that the tandem reaction of metallo carbenoids has evolved as an important strategy in heterocyclic and car-bocycle synthesis. It is a reasonable expectation that future years will see a continued evolution of the cascade chemistry of transition metal carbenoids derived from diazocarbonyls in organic synthesis. As is the case in all new areas of research using catalysts, investigation of the chemistry of these transition metal complexes in the future will be dominated by the search for asymmetric synthesis.
摘要：Radical cyclization of alkenes has become a valuable method for the synthesis of cyclic compounds during the past 30 years. A typical, widely used procedure involves the reduction of a halide or other functional group to a radical with R_3SnH, followed by cyclization and reduction of the resulting radical to a hydrocarbon in the chain propagation steps (eq 1). While this sequence often gives high yields of products, this approach is limited, leading to relatively unfunctionalized products resulting from a net two-electron reduction. Oxidative free-radical cyclization in which the initial radical is generated oxidatively and/or the cyclic radical is terminated oxidatively, has considerable synthetic potential, since more highly functionalized products can be prepared from simple precursors (eq 2).
摘要：Carbopalladation of alkenes, alkynes, allenes, conjugated dienes, and other related π-compounds provides a general, versatile, stereoselective, and chemoselective methodology for carbon—carbon bond formation. In particular, the Heck reaction involving alkenes has been extensively developed and widely used in organic synthesis. Its cyclic version provides attractive routes to common and large rings, and it has recently been applied to the synthesis of natural products and other complex organic compounds. Undoubtedly, many additional applications must be forthcoming. In this connection, further development of both diastereoselective and enantioselective procedures appears to be highly desirable.
摘要：Synthetic organic chemistry has been strongly influenced over the past 20 years by the explosion of two main areas of research, namely: transition metal-mediated synthetic applications and radical-initiated reactions. Both methodologies allow reactions to proceed under mild conditions, with very high selectivities and exhibit great synthetic performance, but they suffer from major drawbacks mainly associated with problems of toxicity and economical standards.
摘要：The construction of multiple carbon—carbon bonds in a single chemical step represents a particularly efficient approach to the synthesis of complex molecular structures. Dramatic examples of the utility of this strategy include (1) the polyene cyclization approach to steroid synthesis as pioneered by Johnson, in which three rings and six contiguous stereogenic centers are established in a single chemical step; (2) the biomimetic synthesis of the Delphi-mium alkaloids by Heathcock; and (3) the intramolecular arene-olefin cyclization, which has been applied by Wender to the exceedingly direct syntheses of a series of polycyclic compounds which are otherwise available only by considerably less efficient pathways.
摘要：One of the initial steps in the development of therapeutic agents is the identification of lead compounds that bind to the receptor or enzyme target of interest. Many analogs of these lead compounds are then synthesized to define the key recognition elements for maximal activity. In general, many compounds must be evaluated in both the lead identification and optimization steps. Increasing burdens have been placed on these efforts due to the large number of new therapeutic targets that continue to be identified thorough modern molecular biology methods.
摘要：This short review covers recent aspects of tandem methodology and its use for the construction of highly functional molecules. The future of organic synthesis lies in efficient methodology and the discovery of new processes for controlling the formation of homochiral centers as well as building up complex chemical architecture using simple techniques. Brevity in organic synthesis is of paramount importance for industry and over the next few years we will see dramatic improvements in this subject and the development of novel catalysts for achieving tandem reactions. Such processes will minimize waste and costs will be kept to a minimum thus increasing efficiency. Organic synthesis remains the key training ground for organic chemists and underpins the economy of this country. We owe much of the modem discoveries in chemistry to the polymer chemists, who were the forerunners of cascade reaction processes.
摘要：The agenda that we undertook some time ago is beginning to pay off in the brief design and execution of synthetic targets. It was stated that the goal of a synthetic craftsman is the provision of realistic amounts of material, and I hope that the examples given in this review conform to that principle. An attempt was made to quantify "somewhat" the type of thought that guides us in designing short and general pathways to various targets, mindful at all times not to overextend the use of any one given method or technique but rather to utilize always the best combination of what is best suited for a particular purpose. The judgment of these accomplishments will be left to future generations.
摘要：The preparation and study of organometallic complexes has fascinated chemists for many years since the preparation of Zeise's salt in 1827. The wealth of knowledge that has been generated has spawned new industries, owing to the exquisite properties and unique transformations that are possible with these species. Moreover the functional group tolerance and the potential for catalytic systems has revolutionized the way we design and conceive synthetic pathways toward organic molecules. The ever increasing demands from society for novel chemical entities with potent biological profiles or diverse functional properties continue to stimulate new science. As we move forward to the next century we can anticipate many exciting developments in chemical synthesis which will advance organic chemistry.
摘要：Outlined here are recent synthetic approaches to conjugated step growth oligomers and polymers that possess precisely controlled lengths and molecular constitutions. The current and potential applications of these new compounds are briefly presented. Coverage of the titled topic is illustrative of current work in the field, and it is not intended to be comprehensive. Extended structures prepared by Langmuir Blodgett or self-assembly techniques, usually resulting in noncovalently linked arrays, will not be discussed. Note that the point at which one refers to a homologous series as an oligomer as opposed to a polymer has been controversial. In fact, different authors have designated values of 20 monomer units, 1000, 6000, or 10 000 Da, as the oligomer/polymer distinction point. The reasons for such demarcations are synthesis or property related, and no definitive segregation points will be inferred in this coverage of the topic.
摘要：Ellagitannins belong to the hydrolyzable tannin class of polyphenol extractives derived from the secondary metabolism of dicotyledonous species of the Angiospermae. Early interest in this class of natural products was confined to the compositional characterization of vegetable tannin extracts used in the leather industry. The first insights into the constitution of the ellagitannins emerged from investigations on the second class of hydrolyzable tannins, the gallbtannins, conducted at the turn of the century by Fischer and Freudenberg. Structural elucidation of numerous members of the ellagitannin family awaited the work of Schmidt and Mayer, whose many contributions to the understanding of both the chemistry and biochemistry of the ellagitannins flourished in the German literature from 1950 onward. However, these seminal studies only revealed the tip of the ellagitannin iceberg, as the vast structural diversity of these complex plant isolates had yet to be appreciated. The lack of adequate isolation/purification and analytical techniques, as well as the absence of universal appeal, thwarted further progress in the chemistry and biochemistry of the ellagitannins at that time. However, recent disclosures of the promising anticancer and antiviral activities of select members of this class of natural products engendered a renaissance of interest in their chemistry. Owing primarily to the efforts of Haslam, Okuda, and Nishioka, and the availability of modern NMR (techniques, over 500 ellagitannins have been struc-turally characterized at present.
摘要：As the examples presented in this review demonstrate, the three-component carbene—alkyne—alkene approach to vinylcyclopropanes allows access to a wide variety of highly functionalized bi- and tricyclic ring systems. Studies completed to date have demonstrated that this reaction is capable of smoothly occurring in a variety of scenarios, though in some cases coordination of additional functionality to the in-situ-generated vinylcarbene intermediate has been shown to inhibit the cyclopropanation step and cause other reaction pathways to be favored.
摘要：Enantioenriched allylic and allenic stannanes serve not only as versatile reagents for the synthesis of important classes of natural products, but also as useful probes of mechanistic details with regard to S_E′ additions and transmetalations of organometallic compounds in general. The principles established with these stable and readily purifiable reagents should be generally applicable to other S_E′ additions as well.
摘要：It is an exciting time for science and one of unprecedented opportunity for chemistry. Over the past two centuries, chemistry has evolved from a relatively isolated pursuit to a position of central importance in the physical and life sciences. It has provided a language and methodology that have unified the sciences in the pursuit of a molecular understanding of our world, thereby shaping the direction, development, and destiny of scientific research. Molecular medicine, molecular biology, and nano (molecular) technology are but a few of the significant scientific fusions that have resulted. From new materials to new medicinal agents, the investment in molecular science has provided returns of fundamental and technological significance, profoundly impacting all facets of our global community.
摘要：In this article, we have discussed the absolute dependence of light for antiviral activity in hypericin and how we are exploiting this dependence, through techniques of synthetic organic chemistry and mo- lecular biology, to produce antiviral agents that are capable of specifically targeting virus-infected cells. We have also discussed the role fo light in generating excited states that possess antiviral activity and the mechanisms by which these excited states may exert this activity. Consequently, the tightly knit combination of the techniques of synthetic organic chemistry, molecular biology and virology, and physical chemistry can be used not only to develop specificity in an antiviral agent but also to provide a basis for modifying and improving this antiviral activity.
摘要：Enzymes are increasingly recognized as useful catalysts for organic synthesis. One of the main attractions for the use of enzymes is their ability to perform reactions in a stereoselective way. Addition-ally, the use of enzymes has several advantages over chemical methods. Because of the mild conditions in enzymatic reactions and the regioselectivity displayed by enzymes, protective group chemistry can be reduced to a minimum. Since most enzymes operate at room temperature in aqueous solution around pH 7, their reactions are often compatible with each other. This makes it possible to combine several enzymes in a one-pot, multistep reaction sequence. Their use in aqueous solution and their biodegradability make enzymes also an excellent environmentally acceptable option. The high regio-and stereoselectivity and catalytic efficiency make enzymes especially useful for the synthesis of complex, highly functionalized molecules like carbohydrates.