Group renaissance

Azirines (three-membered cyclic imines) are related to aziridines by a single redox step, and these reagents can therefore function as precursors to aziridines by way of addition reactions. The addition of carbon nucleophiles has been known for some time [52], but has recently undergone a renaissance, attracting the interest of several research groups. The cyclization of 2-(0-tosyl)oximino carbonyl compounds - the Neber reaction [53] - is the oldest known azirine synthesis, and asymmetric variants have been reported. Zwanenburg et ah, for example, prepared nonracemic chiral azirines from oximes of 3-ketoesters, using cinchona alkaloids as catalysts (Scheme 4.37) [54]. 

In conclusion, the ene reaction has undergone a synthetic renaissance with the advent of Lewis acid and transition metal-catalyzed protocols. The carbonyl-ene, imino-ene, and Alder-ene reactions have all experienced tremendous growth due to the mild conditions in which these reactions can be performed, the high functional group compatibility and high stereoselectivity. As a confirmation of the synthetic utility of the ene reaction, there are many applications to natural product synthesis, and some of these are highlighted in Section 10.12.6. Finally, it should be mentioned that these catalyzed ene reactions are still in their infancy, so much remains to be learned. 

The noticeable renaissance of main group chemistry is well reflected by the relatively large number of structures with main group elements determined by electron diffraction. Consider as examples the molecules with boron, silicon, phosphorus, or sulfur. 

Most inorganic research involves work with small molecules, and relatively little concentrated effort has been devoted to the macromolecular aspects of the subject. The complexity of the macromolecular chemistry has undoubtedly contributed to this neglect. However, it is clear from recent work that dramatic advances in both fundamental science and technology would be possible if the high polymer chemistry of the representative elements were to be studied in detail. Indeed, the much-heralded renaissance in Main Group chemistry may ultimately depend on a closer Investigation of the macromolecular aspects of the field. 

Fassler TF (2001) The renaissance of homoatomic nine-atom polyhedra of the heavier carbon-group elements Si to Pb. Coord Chem Rev 215 347-377... 

In spite of this extreme experimental simplicity, nnderstanding the mechanisms involved in the deposition and the ability to widen the range of deposits obtained—both in composition and the control of numerous other properties—is usually not so simple. Also in spite of its simplicity, it has not been exploited as a techniqne as mnch as might be expected. However, CD has experienced somewhat of a renaissance recently, due largely to its overwhelmingly snccessfnl nse in depositing bnffer layers of CdS (and similar materials) in thin-film photovoltaic cells. The deposition of the CdS, as with many other semiconductors that have been deposited by CD, is often recipe oriented there seem to be almost as many different recipes as there are groups. 

The renaissance of the oriental theme over the past 25 years can be seen as the starting point for a number of new directions in perfumery. One of these, which we saw in the creation of Must de Cartier, has been toward a group of dominantly sandalwood perfumes. Many valuable sandalwood synthetics are now available, including Brahmanol, Sandranol, Madranol, and Sandalore, and these synthetics have been used in conjunction with natural sandalwood in the creation of such perfumes as Joop and Samsara. Another important direction has been toward the so-called floriental perfumes, such as Loulou, which combine the sweetness of an oriental perfume with a floral complex usually based on tuberose. This type of perfume can be seen as a link between the tme orientals and the sweet floral perfumes discussed in the previous section. 

Last I would like to mention the interesting case of two bronze statues. One, Man with a Beard, a handsome Renaissance bronze statue was owned by the Louvre in Paris, whereas the other, Boy with a Ball, was owned by the National Gallery in Washington, D.C. (8). These two statues were remarkably similar in style, and it was suspected that at some time these may have been part of one artifact. Stylistic analysis, however, was not sufficient to make the final decision. X-ray fluorescence study of the two objects showed identical chemical composition which can happen only if they were poured from the same batch of metal. The analysis also showed that by composition the artifacts were closer to brass than to bronze. The group was reunited and is now known as St. Christopher Carrying the Christ Child with the Globe of the World. The statue illustrates the legend in which St. Christopher carried the Christ Child across a river. 

---