Academic literature on the topic '1 ,3-dithiane'

(–)-GB17 3 is one of the Galbulimima alkaloids, a family that shows a wide range of interesting physiological activity. Regan J. Thomson of Northwestern University devised (Angew. Chem. Int. Ed. 2012, 51, 2481) a convergent assembly of 3, a key step of which was the intramolecular Michael cyclization of 1 to 2. The hydroxy aldehyde 6 was prepared by alkylation of the dithiane 4 with 5, followed by hydrolysis. The preparation of 9, by condensation of 8 with 7 followed by hydrogenation and protection, had been reported by Lhommet. Condensation of 9 with the linchpin reagent 10 gave an intermediate keto phosphonate, which was combined with 6 to give, after oxidation, the aldehyde 1. Two new stereogenic centers are created in the course of the cyclization of 1. The authors found that the TFA salt 11 of the Hayashi catalyst delivered 2 with high diastereocontrol. Control experiments showed that the buttressing effect of the dithiane was required for the cyclization. The authors then explored the next intramolecular Michael cyclization of 13 to 14. In this cyclization, the stereogenic center at 6 is in jeopardy by elimination and readdition. Cyclization of the trans unsaturated ester led to the wrong diastereomer of 14, but cyclization of the cis ester 13, prepared by the Still-Gennari protocol, cleanly gave the desired diastereomer. The reaction worked best with the free amine. Under the conditions of the reaction the Michael addition product spontaneously cyclized to the lactam 14. The ketone of 14 was selectively enolized, then converted to its enol triflate, which under Pd-mediated reduction gave the alkene 15. Alkylation of 15 with 16 predominantly gave the diene 18. Hydrolysis of the dithiane to the ketone followed by reduction gave mainly the desired equatorial alcohol, which was cleaved oxidatively to (–)-GB17 3. Although there have been many isolated reports of the utility of intramolecular Michael addition as a synthetic method, there has been little systematic investigation. The optimization studies that are the heart of this work are a welcome addition.

Stephen G. DiMagno of the University of Nebraska developed (Chem. Eur. J. 2015, 21, 6394) a protocol for the clean monoiodination of 1 to 2. The bromomethylation (or chloromethylation, with HCl) of a benzene derivative is straightforward with formal­dehyde and HBr. Naofumi Tsukada of Shizuoka University designed (Organometallics 2015, 34, 1191) a Cu catalyst that mediated the coupling of an alkyne with the benzyl bromide so produced, effecting net propargylation of 3 with 4 to give 5. Triazenes such as 7, versatile intermediates for organic synthesis, are usually prepared by diazotization of the corresponding aniline. Kay Severin of the Ecole Polytechnique Fédérale de Lausanne established (Angew. Chem. Int. Ed. 2015, 54, 302) an alternative route from the aryl Grignard reagent 6. Ping Lu and Yanguang Wang of Zhejiang University showed (Chem. Commun. 2015, 51, 2840) that dimethylformamide could serve as the carbon source for the conversion of 8 to the nitrile 9. Junha Jeon of the University of Texas at Arlington effected (J. Org. Chem. 2015, 80, 4661; Chem. Commun. 2015, 51, 3778) the reductive ortho silylation of 10 to give 11. Vladimir Gevorgyan of the University of Illinois at Chicago found (Angew. Chem. Int. Ed. 2015, 54, 2255) that the phenol derivative 12 could be ortho carboxylated, leading to 13. Lutz Ackermann of the Georg-August-Universität Göttingen, starting (Chem. Eur. J. 2015, 21, 8812) with the designed amide 14, effected ortho metala­tion followed by coupling, to give the methylated product 15. Tetsuya Satoh and Masahiro Miura of Osaka University used (Org. Lett. 2015, 17, 704) the dithiane of 16 to direct ortho metalation. Coupling with acrylate followed by reductive desulfu­rization led to the ester 17. Jin-Quan Yu of Scripps/La Jolla designed (Angew. Chem. Int. Ed. 2015, 54, 888) the phenylacetamide 18 to direct selective meta metalation, leading to the unsat­urated aldehyde 19. In an extension of the Catellani protocol, Guangbin Dong of the University of Texas prepared (J. Am. Chem. Soc. 2015, 137, 5887) the biphenyl 21 by net meta metalation of the benzylamine 20. Several methods for the de novo assembly of benzene derivatives have recently been put forward. Rajeev S. Menon of the Indian Institute of Chemical Technology condensed (Org. Lett. 2015, 17, 1449) the unsaturated aldehyde 22 with the sulfonyl ester 23 to give 24.

Shou-Fei Zhu of Nankai University developed (Angew. Chem. Int. Ed. 2014, 53, 13188) an iron catalyst that effected the enantioselective cyclization of 1 to 2. Bypassing diazo precursors, Junliang Zhang of East China Normal University used (Angew. Chem. Int. Ed. 2014, 53, 13751) a gold catalyst to cyclize 3 to 4. Taking advantage of energy transfer from a catalytic Ir complex, Chuo Chen of University of Texas Southwestern carried out (Science 2014, 346, 219) intramolec­ular 2+2 cycloaddition of 5, leading, after dithiane formation, to the cyclobutane 6. Intramolecular ketene cycloaddition has been limited in scope. Liming Zhang of the University of California Santa Barbara found (Angew. Chem. Int. Ed. 2014, 53, 9572) that intramolecular oxidation of an intermediate Ru vinylidene led to a species that cyclized to the cyclobutanone 8. James D. White of Oregon State University devised (J. Am. Chem. Soc. 2014, 136, 13578) an iron catalyst that mediated the enantioselective Conia-ene cyclization of 9 to 10. Xiaoming Feng of Sichuan University observed (Angew. Chem. Int. Ed. 2014, 53, 11579) that the Ni-catalyzed Claisen rearrangement of 11 proceeded with high diastereo- and enantiocontrol. The relative configuration of the product 12 was not reported. Robert H. Grubbs of Caltech showed (J. Am. Chem. Soc. 2014, 136, 13029) that ring opening cross metathesis of 13 with 14 delivered the Z product 15. Mn(III) cyclization has in the past required a stoichiometric amount of inorganic oxidant. Sangho Koo of Myong Ji University found (Adv. Synth. Catal. 2014, 356, 3059) that by adding a Co co- catalyst, air could serve as the stoichiometric oxidant. Indeed, 16 could be cyclized to 17 using inexpensive Mn(II). Matthias Beller of the Leibniz-Institüt für Katalyse prepared (Angew. Chem. Int. Ed. 2014, 53, 13049) the cyclohexene 20 by coupling the racemic alcohol 18 with the amine 19. Paultheo von Zezschwitz of Philipps-Universität Marburg added (Chem. Commun. 2014, 50, 15897) diethyl zinc in a conjugate sense to 21, then reduced the product to give 22. Depending on the reduction method, either diastereomer of the product could be made dominant. Nuno Maulide of the University of Vienna dis­placed (Angew. Chem. Int. Ed. 2014, 53, 7068) the racemic chloride 23 with diethyl zinc to give 24 as a single diastereomer.

Dithianes such as 1 are readily prepared, from the corresponding ketone or by alkyl­ation. Masayuki Kirihara of the Shizuoka Institute of Science and Technology devel­oped (Tetrahedron Lett. 2013, 54, 5477) an oxidative method for the deprotection of 1 to 2. Konrad Tiefenbacher of the Technische Universität München devised (J. Am. Chem. Soc. 2013, 135, 16213) a hexameric resorcinarene capsule that selectively catalyzed the hydrolysis of the smaller acetal 3 to 4 in the presence of a longer chain acetal. David J. Gorin of Smith College reported (J. Org. Chem. 2013, 78, 11606) the methylation of an acid 5 to 6 using dimethyl carbonate as the donor. Two peroxide-based methods (J. Org. Chem. 2013, 78, 9898; Org. Lett. 2013, 15, 3326) for carboxylic acid methylation (not illustrated) were also recently described. Hisashi Yamamoto of the University of Chicago showed (Angew. Chem. Int. Ed. 2013, 52, 7198) that the “supersilyl” ester 8, prepared from 7, was stable enough to be deprotonated and alkyl­ated, but was easily removed. Michal Szostak and David J. Procter of the University of Manchester uncovered (Angew. Chem. Int. Ed. 2013, 52, 7237) the remarkable cleavage of a C–N bond in an amide 9, leading to the secondary amide 10. This could offer an alternative strategy for difficult-to-hydrolyze amides. Richard B. Silverman of Northwestern University described (J. Org. Chem. 2013, 78, 10931) improved protocols for the formation and removal of the N-protecting 2,5-dimethylpyrrole 11 to give 12. Huanfeng Jiang of the South China University of Technology showed (Chem. Commun. 2013, 49, 6102) that an arenesulfonamide 14 can be prepared by oxidation of the corresponding sodium arenesulfinate 13. Douglas A. Klumpp of Northern Illinois University prepared (Tetrahedron Lett. 2013, 54, 5945) sul­fonamides (not illustrated) by combining a sulfonyl fluoride with a silyl amine. K. Rajender Reddy of the Indian Institute of Chemical Technology developed (Chem. Commun. 2013, 49, 6686) a new route to a urea 17, by oxidative coupling of an amine 15 with a formamide 16.

Benzyl esters are easily deprotected by hydrogenolysis. It is often observed, however, as exemplified by the conversion of 1 to 2 reported (Adv. Synth. Catal. 2008, 350, 406) by Hironao Sajiki of Gifu Pharmacutical University, that alkene hydrogenation can be carried out selectively. Fernando Albericio of the University of Barcelona has developed (Tetrahedron Lett. 2008, 49, 3304) a family of thiophene-based esters 3 that can be removed with acid in the presence of t-butyl esters, and that are stable to the removal of FMOC groups. Vassiliki Theodorou of the University of Ioannina has found (Tetrahedron Lett. 2008, 49, 8230) that esters were rapidly saponified by methanolic NaOH in solvent CH2Cl2. Specific oligosaccharide synthesis depends heavily on the use of orthogonal methods for alcohol protection and deprotection. This is illustrated by the work (J. Org. Chem. 2008, 73, 1008) of Carolyn R. Bertozzi of the University of California, Berkeley, who deployed p-methoxybenzyl (PMB), 3,4-dimethoxybenzyl (DMB), p-chlorobenzyl (PCB) and p-iodobenzyl (PIB) ethers to enable construction of a disaccharide, by way of 9. Piers R. J. Gaffney of Imperial College London has reported (Tetrahedron Lett. 2008, 49, 1836) a practical preparation of the ether 11, that should make this symmetrical protecting group more readily available. George W. J. Fleet of the University of Oxford and Sigthur Petursson of the University of Akureyri have found (Tetrahedron Lett. 2008, 49, 2196) that diphenyl diazomethane 14, easily prepared from benzophenone, reacted under neutral conditions with primary, secondary and tertiary alcohols to form the benzyhydryl ethers. Harsh conditions have often been employed to remove aryl methyl ethers such as 16. Wei Wang of the University of New Mexico and Wenhu Duan of the Shanghai Institute of Materia Medica have developed (Tetrahedron Lett. 2008, 49, 4054) a simple protocol to effect this transformation, by heating the ether to reflux in DMF in the presence of iodocyclohexane 17. Dithianes such as 19 have often been deprotected with stoichiometric heavy metals. Andreas Kirschning of Leibniz Universität Hannover has devised (J. Org. Chem. 2008, 73, 2018) a set of three anionic resins, charged, respectively, with I(O2CCF3 )2 - , HCO3 -, and S2O3 - . Exposure of 19 to the three resins in sequence delivered the very sensitive ketone 20.