Generation and trapping

It is now fairly well established that atomic and few-atom cluster arrays can be generated and trapped in weakly interacting matrices 91), and subsequently scrutinized by various forms of spectroscopy. Up to this time, IR-Raman-UV-visible absorption and emission-esr-MCD-EXAFS-Mossbauer methods have been successfully applied to matrix-cluster samples. It is self-evident that an understanding of the methods of generating and identifying these species is a prerequisite for... 

Generation and trapping of tropothione 29 with dienophiles has been utilized in an approach to partially saturated fused thiophene molecules. For example, treatment of tropone with Lawesson s reagent in benzene, followed by introduction of jV-phenylmaleimide gave the adduct 30 in excellent yield <06TL9329>. 

The generation and trapping of 5,6-bis(trimethylsilyl)benzo[c]furan 126 was reported by Wong utilizing Warrener s s-tetrazine methodology. The trapping of the silylated isobenzofuran with A-phenylmaleimide is illustrated below. A number of other dienophiles such as dimethyl acetylenedicarboxylate, benzoquinone, naphthoquinone and anthra-l,4-quinone have also been used <00TL5957>. 

RIES from diazoalkanes is also sensitive to the dihedral angle between the migrating a-H and the C-N bond of the diazo moiety.57 For example, the A values for the pyridine capture of the photolytically generated carbenes from 46 and 47 are in the ratio of 1.7 1. Similarly, the carbene from 46 is more efficiently generated and trapped in methanol, whereas the photolysis of 47 in methanol affords twice as much olefin (by 1,2-H RIES) compared to the photolysis of 46. These phenomena are attributed to conformational factors that favor RIES during the photolysis of 47, with the proximal excited state represented as a pyramidalized 1,3-C-N=N diradical.57... 

From these examples, one should recognize that the building of the complex steroid skeleton of estrone has been made rather simple when various o-xylylene generation and trapping methods are applied ll5 118). 

Chapter 5 by M. Fujita and T. Okuyama examines the ringopening reactions of alkylidenecyclopropanone acetals for solvolytic generation and trapping of alkylideneallyl cations (resonance hybrids of 1-vinyl-substituted vinyl cations). In Chapter 6 by V. P. Reddy et al. stable ion and computational studies of cyclobutylmethyl cations are discussed. In Chapter 7, G. I. Borodkin and V. G. Shubin discuss and... 

Figure 16. Generation and trapping of Cl2CH-C70+. The plus sign designates the most downfield shifted carbon.

Table 12.16 Effect of inorganic ions on the generation and trapping of arsine...

All tests used 0.1pg of As(lll) in 1ml of 1.5M hydrochloric acid. Optimised hydride generation and trapping conditions were used... 

Scheme 16 Generation and trapping of a thymidine C3, C4 radical cation...

Scheme 17 Radical cation generation and trapping by Norrish type I photofragmentation...

The formulas of the substituted 1,2-cydohexadienes heretofore successfully generated and trapped are collected in Scheme 6.22. It seems that a theoretical study has been performed only with l-phenyl-l,2-cydohexadiene (75), predicting it to be a true allene with a C1-C2-C3 bond angle of 134° [76], which is very similar to that of 6. 

Scheme 6.22 Substituted 1,2-cyclohexadienes that have been successfully generated and trapped.

Scheme 6.51 Generation and trapping of 1,1 -dimethyl-3<52-l H-naphthalene (215) by Miller and Shi.

Miscellaneous. An interesting synthesis of 1,1-difluoro-l-alkenes from ylides and chlorodifluoromethane has been described.47 The ylide acts both as a carbene generator and trapping agent (Scheme 11). 

As an extension of the foregoing studies, the generation and trapping of an HCTD-derived vinyli-denecarbene, i.e., 20 (Scheme 6), was investigated. Thus, reaction of... 

Diazotization of the monoamine in acidic aqueous media formed only the diazoamino compound in high yield. In an attempt to generate and trap 1,2,5-thiadiazyne via diazotization of the 3-amino-4-carboxylic acid in the presence of anthracene, a mixture comprising 9-nitroanthracene and a small amount of 9-thiocyanoanthracene was obtained <71TL2143>. 

The first successful generation and trapping of isomiinchnones using this strategy was described independently by Maier et al. (36,37) and Padwa et al. (38,39). Maier and Evertz (36) were the first workers to report the intramolecular dipolar cycloaddition of isomiinchnones to alkenes, the reaction that Padwa would later exploit so spectacularly. Thus, diazo imide 62 was readily prepared from... 

The newest method for generating isomiinchnones was reported by Padwa and co-workers (40,41). Thus, Kuethe and Padwa developed an exciting new application of the venerable Pummerer reaction of imidosulfoxides to generate and trap isomiinchnones with alkenes. For example, the readily prepared imidosulfoxide 82... 

Padwa utilized this rhodium-catalyzed cyclization of diazothiocarbonyl compounds to great effect in the generation and trapping of thioisomiinchnones (60,61). For example, thioisomiinchnone (101) is readily prepared (and isolated) from the reaction of 2-thiopyrrolidinone and diketene, followed by diazo transfer and rhodium induced cyclization (Scheme 10.18) (60). Trapping with NPM afforded cycloadduct 102. 

As mentioned in Section 10.1.2, Padwa and co-workers (40,41) employed the Pummerer reaction to generate and trap isomtinchnones. This group (190,191) has now adapted the intramolecular version of this tactic to the synthesis of several alkaloids of the pyridine, quinolizidine, and clavine classes. In each case, a 2-pyridone serves as the keystone intermediate. For example, Kuethe and Padwa (190) employed this Pummerer reaction of imidosulfoxides that contain tethered iz-bonds in a formal synthesis of the frog alkaloid ( )-pumiliotoxin C. They also used this methodology to synthesize the azafluorenone alkaloid onychine (295) (Scheme 10.42) (191). Generation of the thionium ion 291 under standard... 

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