Spectroscopic Data and X-Ray Analysis

In solution, multinuclear NMR spectroscopy is by far the most informative technique for analyzing the structure and bonding of phosphinocar-benes. In fact, prior to the synthesis and single crystal X-ray analysis of the (phosphino)(phosphonio)carbene 2d,28 the only spectroscopic evidence for the formation of carbenes came from NMR. 

Classical shielding arguments indicate an electron-rich phosphorus atom, or equally, an increase in coordination number. The silicon atom seems also to be electron-rich, while the carbon has a chemical shift in the range expected for a multiply bonded species. The coupling constant data are difficult to rationalize, as it is not possible to predict the influence of orbital, spin-dipolar, Fermi contact, or higher-order quantum mechanical contributions to the magnitude of the coupling constants. However, classical interpretation of the NMR data indicates that the (phosphino)(silyl)carbenes have a P-C multiple bond character. 

The replacement of the trimethylsilyl group by an isoelectronic, isovalent phosphonio substituent produces the carbene 2d with similar NMR spectroscopic characteristics (Table II). A quick comparison of the reduced 2KPP and 2XPSi coupling constants indicate that these values are also similar. Thus 

Pertinent Chemical Shifts (in ppm) and Coupling Constants (in Hz) for the Phosphinocarbenes and their Diazo Precursors 

The great advantage of the (phosphino)(phosphonio)carbene 2d over its silyl analogues is that it can be crystallized. As we have seen, these two types of phosphinocarbenes are very similar thus, conclusions from the X-ray analysis of 2d28 can probably be extended to the silylcarbenes. Ball and stick views of the molecule are shown in Fig. 2, and the pertinent geometric parameters are in the legend. 

---

A new elegant stereoselective synthesis of humulene (192) has been achieved by a route (Scheme 22) in which the 11-membered-ring framework [cf. (191)] is produced by cyclization of the 11-allylpalladium complex derived from intermediate (190). Buddledin-A (193), -B (194), and -C (195) are new piscicidal sesquiterpenoids which have recently been isolated from the root bark of Buddleja davidiC The caryophyliane framework of these compounds has been established by spectroscopic data and X-ray analysis of the mono-bromohydrin (196) derived from buddledin A (193). An extension of previous studies on the cyclization of the epoxy-ketone (197) derived from caryophyllene has shown that the base-catalysed cyclization of the isomeric epoxy-ketones (198) and (199) provides compounds... 

X-ray crystallography [171]. The dihydrophenanthropyrans, shanciol (439) [200] and shanciols C-F (440-443) [108,117], can be considered as hybrids of phenanthrene with flavan. Shanciol (439) was elucidated on the basis of spectroscopic data and X-ray analysis. The absolute configurations of the known dihydrophenanthropyran-bletilol B were also determined [200]. 

A series of lycoposerramines isolated by Takayama et al. were fawcettimane-type and fawcettidane-type alkaloids from the same species Lycopodium serratum in Japan which contains huperzines in China. The structure of lycoposerramine-A (21), which has a l,2,4-oxadiazolidin-5-one residue in the molecule, was elucidated through spectroscopic data and X-ray analysis (31,32). Seven new alkaloids, lycoposerramines B (22), C (23), D (24), E (25), P (26), Q (27), S (28), and U (29), with novel, fawcettimine-related structures were isolated from the club moss Lycopodium serratum in Japan (33). Their relative and absolute stereochemistries were analyzed by spectroscopic data. X-ray analysis, and chemical correlations. The skeleton of lycoposerramine A (21) may be constructed by the incorporation of NH3, NH2OH, and a Ci unit into a fawcettimine-type skeleton. 

Similar conversions of cyclopropenes can be achieved with other metal complexes. In the presence of trialkylphosphane-modified Pd(0) catalysts, 3,3-dimethylcyclopropene was quantitatively and stereoselectively cyclotrimerized to give 3,3,6,6,9,9-hexamethyl-c ,c/i,/ran -tetra-cyclo[6.1.0.0 0 ]nonane (14). The structure was derived from spectroscopic data and X-ray crystal analysis. The product undergoes thermal rearrangement to form 3,3,6,6,9,9-hexamethyl-trun. -tricyclo[6.1.0.0 ]non-4-ene (15). ° This method has been extended to other 3,3-disubstituted cyclopropenes. ... 

In the course of reduction experiments of methyl 12,14-dinitrodehydroabietate 3, a new benzoxazole resin add derivative 6 was synthesized and its structure established by spectroscopic data, chemical derivatization and X-ray analysis. 

The structure and absolute configuration of pinguisone (333) have been determined by a combination of spectroscopic data (m.s. and 13Cn.m.r.) and X-ray analysis of its p-bromobenzylidene derivative.140... 

Iridium chemistry also holds a rare example of a monodentate guanidinate ligand. The monomeric parent amido complex Cp Ir(PMe3)(Ph)(NH2) cleanly undergoes an insertion reaction on treatment with diisopropylcarbodiimide (Scheme 153). Spectroscopic data and an X-ray structural analysis revealed the presence of a nonchelating guanidinate ligand. ... 

The gross structure of 73 was determined by a combination of spectroscopic and chemical means (112) stereochemistry was proved by single-crystal X-ray diffraction (113). Much later, 73 was also found in C. guianensis from Brazil (114). It was characterized by PMR and CMR data as well as by X-ray analysis. Gerrardine showed activity against Salmonella spp. (115), Candida albicans T.A., Escherichia coli, and Klebsiella pneumoniae D.T. (114). 

The deshielded 31P and 13C NMR chemical shifts observed for 41-43 ( 31P +130, 13C +76, /PC 85 Hz) are consistent with the presence of a P = C double bond and positive charge development at phosphorus these spectroscopic data are in fact very similar to those observed for the methylenephosphonium salt 40.59,6° This similarity is reinforced by the X-ray analysis of the gallium adduct 42 (Fig. 4) (i) The phosphorus and carbon atoms adopt a trigonal planar geometry, (ii) there is a twist angle between the two planes of 34.1°, and (iii) the phosphorus-carbon bond distance is rather short (1.61 A). 

Sulfircin (369), an antifungal sesterterpene sulfate was isolated as the iV,iV-dimethylguanidinium salt from a deepwater Ircinia species and its structure was determined by X-ray analysis [324]. Two sesterterpene sulfates, hipposulfates A (370) and B (371), were isolated from Hippospongia cf. metachromia from Okinawa and their structures were elucidated by interpretation of spectroscopic data. Both compounds possess an enolsulfate functionality [325]. 

Azetidine-2-carboxylic acid (2) like proline gives an intense blue color with sodium nitroprusside in 10% acetaldehyde solution in the presence of sodium carbonate. 98,99 Upon usual acid hydrolysis (6M HC1, 110 °C, 24 h or more) as required for amino acid analysis, azetidine-2-carboxylic acid is completely decomposed, yielding mainly homoserine lactone, as well as other ninhydrin-positive compounds. 87,89,99 To enable an accurate quantification of this imino acid, azetidine-2-carboxylic acid peptides should be hydrolyzed by alkali (5M barium hydroxide, at 100 °C for 18 h 89 or 2 M sodium hydroxide at 110°C for 22h 100 ). There are extensive NMR spectroscopic data available 100-104 and the absolute configurations of A-acetyl-L-azetidine-2-carboxylic acid 105 and A-terf-butoxycarbonyl-L-azetidine-2-car-boxylic acid 106 have been determined by X-ray analysis. 

---