“…The synthesis of methyl ketone 7 is summarized in Scheme . Brown's asymmetric methallylation 7 of aldehyde 4 , which was prepared from d -mannitol according to the literature report, produced homoallylic alcohol 5 (>97:3 by 1 H NMR) in 75% yield. 2 Synthesis of Methyl Ketone 7 …”
[reaction: see text] Enantioselective synthesis of 3, a revised structure for clavosolide A, was completed. Both (1)H and (13)C NMR spectra of the natural and synthetic compounds were identical, and optical rotation measurements identified the absolute configuration of the natural clavosolide A as [corrected] 3.
“…The synthesis of methyl ketone 7 is summarized in Scheme . Brown's asymmetric methallylation 7 of aldehyde 4 , which was prepared from d -mannitol according to the literature report, produced homoallylic alcohol 5 (>97:3 by 1 H NMR) in 75% yield. 2 Synthesis of Methyl Ketone 7 …”
[reaction: see text] Enantioselective synthesis of 3, a revised structure for clavosolide A, was completed. Both (1)H and (13)C NMR spectra of the natural and synthetic compounds were identical, and optical rotation measurements identified the absolute configuration of the natural clavosolide A as [corrected] 3.
“…Compared to literature procedures, Swern oxidation of the dioxolane on a large scale afforded variable yields (20‐45 %) of the favored “oxo‐product”, always containing a considerable amount of dimethyl sulfite as a by‐product (∼30 % content was observed by NMR after purification). The worst results were observed in oxidation with PCC or in cleavage of D‐mannitol with lead tetraacetate . Additionally, subsequent fluorination proceeded to give very low preparative yields of the corresponding difluorinated product (∼12 %).…”
A novel efficient method for the synthesis of gem‐difluorinated derivatives of acyclic nucleotide analogues has been developed. The method is based on utilization of diethyl difluoromethylphosphonate as a nucleophilic difluoromethylation reagent. In contrast to previous difluoromethylation procedures using commercially available DAST or deoxofluor, this process is very robust, proceeds under mild conditions and is accompanied only by small amounts of by‐products. The reaction of diethyl difluoromethylphosphonate with 2‐benzyloxyacetaldehyde afforded 3‐(benzyloxy)‐1,1‐difluoropropan‐2‐ol (6) a key precursor for syntheses of difluoromethylated analogues of various acyclic nucleoside phosphonates.
“…The required stereochemistry was successfully installed using a chelation-controlled glycolate CR followed by RCM (Scheme 56). 66 A formal synthesis of (-)-perhydrohistrionicotoxin via Ireland CR and RCM as key steps has been reported by Kim and coworkers. 67 The interesting feature of this sequence is the creation of stereogenic centres for the construction of the azaspirocyclic skeleton.…”
Section: Design Of Heterocyclics and Carbocyclics By Chelated Cr And Rcmmentioning
Olefin metathesis promoted by a well-defined metal carbene complex has evolved into an efficient method for the construction of a broad range of carbocyclic and heterocyclic rings of varying size. The synthetic potential of the olefin metathesis has been further increased by combining various other C-C bond forming processes either in tandem or in sequence. Herein, application of Claisen rearrangement and olefin metathesis to prepare various intricate and/or biologically important targets has been described.
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