Dicarba synthesis

Total synthesis of (+)-validamycins A and B starting from a common synthetic intermediate was elaborated by the following sequence. Tetra-(9-benzyl-(-l-)-valienamine (370), derived from 211, and the di-O-benzyl derivative (371) of the epoxide were coupled in 2-propanol to produce the protected dicarba compound (374), the structure of which was confirmed by conversion into (-1-)-validoxylamine B nonaacetate. Concurrently, compound 372 was glycosylated and the product oxidized with a peroxy acid, to afford a mixture of products from which the desired epoxide (373) was obtained in 70% yield. Coupling of 370 with 373 in 2-propanol at 120° afforded two carba-trisaccharides, and the major product (47%) was depro-tected and characterized as the dodecaacetate of validamycin B. The pro-... 

Synthesis and characterization of gold-(l) and -(111) complexes with l-methyl-2-sulfanyl-l,2-dicarba-closo-dodecaborate. Journal of the Chemical Society, Dalton Transactions, (17), 2963-2967. 

The chemistry of titanium has been reviewed in COMC (1982) and COMC (1995)40 41 as well as in Comprehensive Coordination Chemistry II. 2 Since then, several contributions have covered the coordination chemistry of cyclopenta-dienyltitanium carboxylates and related complexes,43 new titanium imido chemistry,44 the use of titanium(iv) chloride45 and isopropoxide46 in stereoselective synthesis, the preparation and synthetic applications of l, -dicarba-nionic titanium intermediates47 and organotitanium complexes,48 49 and titanium-catalyzed enantioselective... 

An excellent review including research on the intermediate dicarba-wido-boranes has been compiled by Plesek and Hermanek 113b). Many other new compounds are revealed. Previously, they had reported (113) the high yield synthesis of 5,6-C2BgHi2 (XI- and XVI-NlO). 

In the early synthesis of deamino-dicarba-oxytocin, the intermediate Z-Asu(OMe)-OH was used which requires a saponification step prior to cyclizationJ1-2 Subsequently, a synthesis more consistent with the general protection strategies in peptide synthesis was developed with the intermediate Z-Asu(OtBu)-OH.12,24 As outlined in Scheme 9, upon selective deprotection of the side-chain carboxy group of the Asu residue by exposure to TFA, the octapeptide derivative 26 is converted into the 2,4,5-trichlorophenyl ester 27 using the tri-fluoroacetate method.129,20 Hydrogenolytic Na-deprotection of 27 in dilute solution leads to... 

The constituent amino acid of dicarba-analogues of cystine is L,L-2,7-diaminosuberic acid [(2S,7S)-2,7-diaminooctanedioic acid, 29, n = 4]. Despite the simplicity of this structure (Scheme 12), the two amino and two carboxy groups must be selectively protected for convenient application in solution and/or solid-phase peptide synthesis. 

Bampos and coworkers (10ACI3930) have reported the synthesis of a new indene expanded porphyrin also called [22]dibenzo-dicarba-hexa-phyrin (1.0.0.1.0.0) 121 (Scheme 49) by "2+2" acid-catalyzed condensation of (S-alkyl-substituted dipyrromethanes 119 with 2-ethynyl-benzaldehyde 120. 

Scheme 49 "2+2" Condensation approach for the synthesis of [22]dibenzo-dicarba-hexaphyrin.

The rearrangements mechanism and the sequence of cage atoms migrations were proved unequivocally by carrying out the reactions with selectively deuterated 7,8-dicarba-nido-undecaborates(l-), the use of nB and H NMR spectroscopy and X-ray structures, as well as the counter synthesis of a rearrangement product. 

In order to confirm the formation of 8-alkyl-7,9-dicarba- irfo-undecaborate(l-) its counter synthesis was undertaken.10 For this purpose the dicarbollide, prepared from 7,9-dicarba-nirfo-undecaborate( 1 -) was introduced into the reaction with n-butyl boron... 

Coordination chemistry of boranes and heteroboranes is a major field of research in cluster science. By far the most extensively studied clusters are the eleven vertex carboranes dicarba-nicfo-undecaborane, carba-mt/o-undecaborane and the six vertex carborane dicarba-m fifo-hexaborane. The synthesis of the elven vertex silaborate [MeSiBioHu] prompted us to study the coordination abilities of this cluster towards transition metals. In... 

P. T. Brain, J. Cowie, D. J. Donohoe, D. Hnyk, D. W. H. Rankin, D. Reed, B. D. Reid, H. E. Robertson, A. J. Welch, M. Hofmann, P. v. R. Schleyer. 1-Phenyl-1,2-dicarba-ctoso-dodeca-borane, l-Ph-l,2-c/oso-C2BioHn. Synthesis, characterization, and structure as determined in the gas phase by electron diffraction, in the crystalline phase at 199 K by X-iay diffraction, and by ab initio computations. Inorg. Chem. 35, 1701-1708 (1996). 

An RCM approach in conjunction with microwave heating has found other applications in cyclic peptide synthesis. Novel A-chain dicarba analogs of human relaxin-3 (H3 relaxin, INSL7) have been prepared and found to have applications in the treatment of stress and obesity. Artificial a-helices that feature a dicarba... 

Just recently a [2+2] methodology has been described (07JA13800, 08M11), which enables the synthesis of fld/-diazuliporphyrins (dicarba-porphyrinoid systems with two adjacent azulene subunits) by the condensation of dipyrrylmethanes with diazulene dialdehydes. 

R 299 A. Sterzik, I. Maulana, S. Blaurock, P. Loennecke, E. Rys, V.N. Kalinin and E. Hey-Hawkins, Synthesis of Rac- and Meso-l,2-bis(tert-butyl-chlorophosphino)-1,2-dicarba-closo-dodecaborane( 12) and Transition-Metal Complexes Thereof, p. 85... 

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