Synthesis in General

Two illustrations that show the power of this reaction for the preparation of strained cycloalkenes are the contractions of 102 to the propellane 103 , an application that has been reviewed , and of 104 to the bicyclo[2.1.1]hexene 105 . The utility of the Ramberg-Backlund rearrangement in the preparation of various natural products such as steroids , terpenoids and pheromones has been demonstrated. In addition to the synthetic applications mentioned in the previous subsection, several selected examples taken from the recent literature are given in equations 66-69. These examples further demonstrate the potential of this method for alkene synthesis in general. 

The synthetic utility of the remarkably facile and efficient [2,3]-sigmatropic rearrangement of propargylic sulfenates has been further demonstrated in a variety of preparations and interesting reactions of allenyl sulfoxides , including the preparation of vinylallenes " which are useful intermediates in organic synthesis in general and natural polyenes, such as Vitamins A and D, in particular Two typical examples, taken... 

The same reasoning applies to the synthesis of pure enantiomers as to organic synthesis in general processes should be atom efficient and have low E factors, i.e. involve catalytic methodologies. This is reflected in the increasing attention being focused on enantioselective catalysis, using either enzymes or chiral metal complexes. 

We are concerned only with EROS, a unique system for such studies, and this article is in no way an overall review of computer-aided synthesis in general. 

The chemistry of iron has been reviewed in COMC (1982) and COMC (1995)312-314 as well as in Comprehensive Coordination Chemistry 7/.315 More recent reviews cover iron-catalyzed transformations with samarium(ll) iodide,18d the chemistry of tricarbonyliron-diene complexes,316 and iron-catalyzed reactions in organic synthesis in general.317... 

One reaction characteristic of phase 1 metabolism is monooxygenase-catalysed hydroxy-lation at specific C—H bonds without chemical activation. Different enzymes show varying degrees of regio-, chemo-, and enantio-specificity, so the reaction is usually challenging for the synthetic chemist to reproduce once preparation of such a metabolite is required. It should be evident that biocatalysts with such capabilities would also be highly desirable as tools for chemical synthesis in general. 

The Michael addition has attracted enormous attention as one of the most important G-G bond-forming reactions in solution-phase organic synthesis. In general. 

The catalytic asymmetric epoxidation of a,p-unsaturated aldehydes has also been an important challenge in iminium catalysis and for chemical synthesis in general. More recently, Jprgensen and coworkers have developed an asymmetric organocatalytic approach to ot, (3-epoxy aldehydes using pyrrolidine catalyst 20 and H2O2 as the stoichiometric oxidant. The reaction appears to be extremely general and will likely receive wide attention from the chemical synthesis community (Scheme 11.6b). 

Alkynes, although not as prevalent as alkenes, have a number of important uses in synthesis. In general, alkynes are somewhat less reactive than alkenes toward many electrophiles. A major reason for this difference in reactivity is the substantially higher energy of the vinyl cation intermediate that is formed by an electrophilic attack on an alkyne. It is estimated that vinyl cations are about lOkcal/mol less stable than an alkyl cation with similar substitution. The observed differences in rate of addition in direct comparisons between alkenes and alkynes depend upon the specific electrophile and the reaction conditions.111 112 Table 4.4 summarizes some illustrative rate comparisons. A more complete discussion of the mechanistic aspects of addition to alkynes can be found in Section 6.5 of Part A. 

We hope that this book will be useful and a source of inspiration for all those interested in the chemical, biological and technical aspects of asymmetric synthesis in general and will stimulate new ideas and research activities among the young scientists in this rapidly growing field. 

Metal-catalyzed olefin metathesis had an enormous impact on organic synthesis in general. Extensive research on mechanistic aspects (3,4) and the development of catalysts has been performed, which culminated in the award of the Nobel Prize for Chemistry in 2005 to Chauvin, Grubbs and Schrock. 

Microwave-assisted synthesis in general is likely to have a tremendous impact in the medicinal/combinatorial chemistry communities because it shortens reaction times, improves final yields and purities, and can carry out reactions that previously were thought impossible to do. It should be stressed that in general the rate enhancements seen in microwave-assisted synthesis can be attributed to the very rapid heating of the reaction mixture (flash heating) and the high temperatures that can be reached, rather than to any other specific or nonthermal microwave effect.40... 

Rodet et al., 1989] Rodet, X., Potard, Y., and Barriere, J. (1989). The CHANT Project From the Synthesis of the Singing Voice to Synthesis in General. In Roads, C., editor, The Music Machine, pages 449-465. MIT Press, Cambridge, MA. 

As dedicated microwave instruments appeared rather recently on the market and several interesting applications of microwave irradiation for natural product synthesis were described applying domestic microwave ovens, we decided to include also research performed with domestic ovens, although one could argue that some of these experiments lack reproducibility. On the other hand, the development of safe and reproducible synthetic routes for domestic instruments, which are cheap and at the disposal of every research lab all over the world, is a challenge worth the task as this should tremendously speed up the introduction of microwave irradiation in organic synthesis in general. 

Another aid to understanding heterocyclic synthesis in general is the fact that a large number of five- and six-membered heterocycles can be constructed from various combinations of small acyclic molecules by complementary matching of nucleophilic and electrophilic functionality. 

This near constancy of the unit cost of essergy vs. steam temperature and pressure led naturally to Boteler s "Utilization Function" (27), which appears in Requirements 2 and 3 of the following paragraph. In view of these contributions by Smith and Boteler, a description of essergetic functional analysis may now be presented which is expected to be applicable to process design and synthesis in general ... 

The same reasoning applies to the synthesis of pure enantiomers as to organic synthesis in general for economic and environmental viability, processes should... 

Many new developments in cationic polymerizations and in polymer synthesis in general are due to the synthesis of new monomers and therefore new polymers with novel properties. However, the most significant developments are in more controlled polymerizations that enable the synthesis of materials with well-defined properties. After a brief introduction to polymer synthesis, we will focus on syntheses involving only cationic intermediates. Much of the basis of this chapter is covered in general... 

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