Mesylates based-induced

Glycals are also available from 2-deoxy sugars by acid- or base-induced eliminations ofanomeric substituents. These methods are limited by the availability ofthe 2-deoxy sugars, for which the glycals themselves are the most obvious synthetic precursors. However, examples of these methods (Scheme 5.43) are in the direct preparation oftri-O-benzyl-D-glucal (14) from 2-deoxy-tri-O-benzyl-D-glucopyranose (13) via its 1-O-mesylate [117], and di-O-benzyl-D-ribal (16) from the phenylselenide 15 via oxidation to the selenoxide followed by elimination [118]. 

The past few years have witnessed a considerable effort by several research groups to effect stereoselective syntheses of appropriately substituted hydroazulenes. Recently some new approaches to this problem have been reported. Marshall and Huffman, for instance, have found that treatment of the enone-mesylate (395) with diborane followed by base-induced fragmentation of the intermediate boronate (396) yielded the cyclodecadienol (397) in 60 % yield. Solvolysis of the p-nitrobenzoate of (397) in aqueous dioxan containing sodium bicarbonate afforded the hydroazulenol (398) in 70 % yield. The high degree of stereoselectivity in this reaction is rationalized on the basis of the preferred mode of cyclization of the allylic cation (399). To date, the solvolytic routes to hydroazulenes have... 

The synthesis of stereodefined acyclic alkenes via 3-elimination reactions—such as (1) dehydration of alcohols, (2) base-induced eliminations of alkyl halides or sulfonates (tosyl or mesyl esters), and (3) Hofmann eliminations of quaternary ammonium salts—often suffers from a lack of regio- and stereoselectivity, producing mixtures of isomeric alkenes. 

The simpler enediyne 103 could not be synthesized, since any attempt to exploit the usual cyclization of an acetylide onto a carbonyl moiety failed, giving a dimeric derivative arising from an intramolecular double coupling as the only product. This problem was solved using a different chromium(II)-mediated cyclization, followed by the base-induced elimination of mesylate... 

The structure and absolute stereochemistry of hinesol (282) has now been firmly established by an unequivocal synthesis which involved the tricyclic dienone (329) prepared from 6-methoxy-l-tetralone. Treatment of the dienone with lithium dimethylcopper gave a mixture of syn and anti enones (330). By a series of stereoselective reactions this compound was converted to the diol (331) whose mono-mesylate underwent a base-induced cleavage to give the spiro[4,5]-ketone (332). Elaboration of this ketone to hinesol was accomplished along... 

Michael acceptors and other activated alkenic double bonds can play the role of electrophilic components in the cyclization of piperidine derivatives to quinolizidines. For example, base-induced )S-elimination of the mesylated alcohol (198) gave the epilupinine precursor (199) (Scheme 35)... 

Simple mercury(ii)-catalysed cyclization of pent-4-ynoic acid gives y-methyl-enebutyrolactone (c/. 3, 71), the enolate of which, on condensation with aldehydes followed by mesylation and base-induced elimination, affords a-alkylidene derivatives in moderate yields (Scheme 19). This method has been used to prepare deoxyobtusilactone, a relative of some naturally occurring cytotoxic lactones. 

The mass spectra of l-acyl-l//-l-benzazepines have been recorded.23 The mass spectrum of 3-mesyl-3/7-3-benzazepine shows an intense base peak at m/e = 142duetothebcnzazepinylium ion and a peak (51 %) at m/e — 115 (-HCN) which is attributed to the indenium cation.26 Fragmentation patterns for 1H- and 5/7-2-benzazepines40 and for 5//-dibenz[c,e]azepine5 are available. The electron-impact induced fragmentation pattern of 5//-dibenz[6,/]azepine displays an intense molecular ion as the base peak, and a moderately intense (M + 1) peak.5 ... 

Transformation of bromocriptine free base 2 into water soluble salt -mesylate, is the only way to obtain a suitable therapeutical form. Crystallization of mesylate using alcohol as a solvent in the presence of excess of strong acid, e.g. methanesulphonic acid can induce formation of 12 -0-alkyl-derivative 2. Until now this derivatisation of ergot molecule has been practically unknown. In continuation we developed the preparative method for obtaining these compounds, (using tetrafluoroboric acid as a catalyst) (ref. 20). 

Inhibitors specific for PKC-p have a more favorable toxicity profile. In fact, in a study by Aiello et al. (52), the effect of VEGF on retinal vascular permeability appeared to be mediated predominantly by the p-isoform of PKC. There was >95% inhibition of VEGF-induced permeability after administration of a PKC p-isoform-selective inhibitor (50). Studies are currently being conducted with a new PKC-p inhibitor, known as ruboxistaurin mesylate. Thus far, based on animal... 

Release of compounds from polymer-bound carbamates has not to be performed via nucleophilic attack but can also be induced by the addition of acids like, for example, TFA in various concentrations. The released target compounds are either primary or secondary amines. The synthesis described in Scheme 34 has been recently published by DoUe et al. [183]. Synthesis of piperazines 227 has been conducted on a or-methylbenzyl resin 223 that has been activated with 4-NPCF and that has been fmther reacted with diethanolamine 224. After mesylation of the two resulting terminal hydroxy groups, reaction with a primary amine 226 and base gave immobilized piper-... 

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