Academic literature on the topic 'Alcohols. Grignard reagents'

Oxygenated secondary stereogenic centers are readily available. There is a limited range of carbon nucleophiles that will displace a secondary leaving group in high yield with clean inversion. Teruaki Mukaiyama of the Kitasato Institute has described (Chem. Lett. 2007, 36, 2) an elegant addition to this list. Phosphinites such as 1 are easily prepared from the corresponding alcohols. Quinone oxidation in the presence of a nucleophile led via efficient displacement to the coupled product 2. The sulfone could be reduced with SmI2 to give 3. Enantioselective reduction of trisubstituted alkenes is also a powerful method for establishing alkylated stereogenic centers. Juan C. Carretero of the Universidad Autonoma de Madrid has found (Angew. Chem. Int. Ed. 2007, 46, 3329) that the enantioselective reduction of unsaturated pyridyl sulfones such as 4 was directed by the sulfone, so the other geometric isomer of 4 gave the opposite enantiomer of 5. The protected hydroxy sulfone 5 is a versatile chiral building block. Samuel H. Gellman of the University of Wisconsin has reported (J. Am. Chem. Soc. 2007, 129, 6050) an improved procedure for the aminomethylation of aldehydes. L-Proline-catalyzed condensation with the matched α-methyl benzylamine derivavative 7 gave the aldehyde, which was immediately reduced to the alcohol 8 to avoid racemization. The amino alcohol 8 was easily separated in diastereomerically-pure form. In the past, aldehydes have been efficiently α-alkylated using two-electron chemistry. David W. C. Macmillan of Princeton University has developed (Science 2007, 316, 582; J. Am. Chem. Soc. 2007, 129, 7004) a one-electron alternative. The organocatalyst 9 formed an imine with the aldehyde. One-electron oxidation led to an α-radical, which was trapped by the allyl silane (or, not pictured, a silyl enol ether) leading to the α-alkylated aldehyde 10. This is mechnistically related to the work reported independently by Mukund P. Sibi (J. Am. Chem. Soc. 2007, 129, 4124; OHL Feb. 11, 2008) on one-electron α-oxygenation of aldehydes. Secondary alkylated centers can also be prepared by SN2’ alkylation of prochiral substrates such as 11. Ben L. Feringa of the University of Groningen has shown (J. Org. Chem. 2007, 72, 2558) that the displacement proceeded with high ee even with conventional Grignard reagents.

Mohammad Navid Soltani Rad of Shiraz University of Technology has shown (Tetrahedron Lett. 2007, 48, 6779) that with tosylimidazole (TsIm) activation in the presence of NaCN, primary, secondary and tertiary alcohols are converted into the corresponding nitriles. Gregory C. Fu of MIT has devised (J. Am. Chem. Soc. 2007, 129, 9602) a Ni catalyst that mediated the coupling of sp3-hybridized halides such as 3 with sp3-hybridized organoboranes such as 4, to give 5. Usually, carbanions with good leaving groups in the beta position do not couple efficiently, but just eliminate. Scott D. Rychnovsky of the University of California, Irvine has found (Organic Lett . 2007, 9, 4757) that initial protection of 6 as the alkoxide allowed smooth reduction of the sulfide and addition of the derived alkyl lithium to the amide 7 to give 8. Doubly-activated Michael acceptors such as 11 are often too unstable to isolate. J. S. Yadav of the Indian Institute of Chemical Technology, Hyderabad has shown (Tetrahedron Lett. 2007, 48, 7546) that Baylis-Hillman adducts such as 9 can be oxidized in situ, with concomitant Sakurai addition to give 12. Rather than use the usual Li or Na or K enolate, Don M. Coltart of Duke University has found (Organic Lett. 2007, 9, 4139) that ketones such as 13 will condense with amides such as 14 to give the diketone 15 on exposure to MgBr2. OEt2 and i -Pr2 NEt. Simultaneously, Gérard Cahiez of the Université de Cergy (Organic Lett. 2007, 9, 3253) and Janine Cossy of ESPCI Paris (Angew. Chem. Int. Ed. 2007, 46, 6521) reported that Fe salts will catalyze the coupling of sp2 -hybridized Grignard reagents such as 17 with alkyl halides. John Montgomery of the University of Michigan has described (J. Am. Chem. Soc. 2007, 129, 9568) the Ni-mediated regio- and enantioselective addition of an alkynes 20 to an aldehyde 19 to give the allylic alcohol 21. In a third example of sp2 - sp3 coupling, Troels Skrydstrup of the University of Aarhus has established (J. Org. Chem. 2007, 72, 6464) that Negishi coupling with alkenyl phosponates such as 23 proceeded efficiently.

Nobuaki Kambe of Osaka University found (Tetrahedron Lett. 2009, 50, 5644) that with a Ni catalyst, Grignard reagents coupled preferentially with primary alkyl iodides, even in the presence of the usually reactive ketone. Maurice Santelli of the Université d’Aix-Marseille devised (Tetrahedron Lett. 2009, 50, 5238) a protocol for the conversion of a ketal 4 to the doubly homologated product 6. Brian T. Gregg of AMRI established (Tetrahedron Lett. 2009, 50, 3978; Tetrahedron Lett. 2009, 50, 7070) a procedure for the homologation of a nitrile 7 to the amine 9. Replacement of the NaBH4 with a second Grignard reagent led to the α-quaternary amine (not shown). Toshiaki Murai of Gifu University independently developed (J. Org. Chem. 2009, 74, 5703) a protocol for coupling two Grignard reagents with the linchpin reagent 11 to give the amine 12. Laurel L. Schafer of the University of British Columbia demonstrated (Angew. Chem. Int. Ed. 2009, 48, 8361) Ta-catalyzed intramolecular addition of a methyl amine 14 to the terminal alkene 13 to give 15. Jason S. Kingsbury of Boston College extended (Organic Lett. 2009, 11, 3202) the Roskamp protocol to unstable diazo alkanes such as 17, to give 18. Katsukiyo Miura of Saitama University found (Organic Lett. 2009, 11, 5066) that Pt catalyzed the branched addition of a terminal alkenyl silane 19 to an aldehyde 16 to give the branched adduct 20. Silanes such as 19 are readily prepared directly from the corresponding terminal alkene. Kálmán J. Szabó of Stockholm University observed (J. Org. Chem. 2009, 74, 5695) that the allyl boronate derived from the allylic alcohol 21 could add to the aldehyde 23 to give, depending on the solvent, either the branched product 24 or the linear product 25. The Wittig reaction is a major producer of by-product waste in chemical synthesis. Yong Tang of the Shanghai Institute of Organic Chemistry found (J. Org. Chem. 2007, 72, 6628) that Ph3As could serve catalytically in the condensation of 26 with an aldehyde. Christopher J. O’Brien of the University of Texas at Arlington and Gregory A. Chass of the University of Wales described (Angew. Chem. Int. Ed. 2009, 48, 6836) a related procedure using a cyclic phosphine.

Luigino Troisi of the University of Salento found (Tetrahedron Lett. 2010, 51, 371) that a variety of primary and secondary amines could be coupled with a benzylic halide 1 under carbonylating conditions. Ilhyong Ryu of Osaka Prefecture University showed (Organic Lett. 2010, 12, 1548) that under reducing conditions, an iodide 3 coupled with CO to give the primary alcohol. Felicia A. Etzkorn of Virginia Tech observed (Organic Lett. 2010, 12, 696) that under Hg hydrolysis conditions, the orthothioester derived from 5 coupled with 6 to give 7. Yasuharu Yoshimi of the University of Fukui and Minoru Hatanaka of Iwate Medical University devised (Tetrahedron Lett. 2010, 51, 2332) conditions for the decarboxylative addition of the acid 8 to 9 to give 10. Yong-Min Liang and Xiaojun Yao of Lanzhou University and Chao-Jun Li of McGill University described (J. Org. Chem. 2010, 75, 783) a related procedure with α-amino acids. Yasutaka Ishii of Kansai University established (J. Am. Chem. Soc. 2010, 132, 2536) that t -butyl acetate 12 was an effective partner for the Ir-mediated oxidation-coupling-reduction of an alcohol 11. He used (J. Org. Chem. 2010, 75, 1803) a similar protocol to condense acetone with the diol 14, to give the long-chain diketone 16. The formation of allylic Grignard reagents can be inefficient because the excess reactive halide tends to couple with the Grignard reagent as it forms. Brandon L. Ashfeld of the University of Notre Dame found (Tetrahedron Lett. 2010, 51, 2427) a simple solution to this problem: inclusion of a catalytic amount of the inexpensive Cp2 TiCl2 to mediate the addition of 18 to 17. Brian T. Connell of Texas A&M University demonstrated (J. Am. Chem. Soc. 2010, 132, 7826) that with Mn, 21 could be added to 20. The acetate 21 is thus an easily prepared homoenolate equivalent. Note that although 21 is an E/Z mixture, the product 22 is cleanly Z. Gérard Cahiez of the Université de Paris 13 reported (Synlett 2010, 299) a detailed study of the Cu-catalyzed coupling of 24 with 23. Without supporting ligands, slow addition (syringe pump, 1 h) of 24 to 23 assured clean formation of 25. Manual slow addition (dropping funnel, 15 min) was not effective.

( + )-Discodermolide 3, a potent anticancer agent that works synergistically with taxol, may yet prove to be clinically effective. For the synthetic material to be affordable, a highly convergent synthesis is required. Jean-François Betzer and Janick Ardisson of the Université de Cergy- Pontoise have described (Angew. Chem. Int. Ed. 2007, 46, 1917) such a synthesis, coupling 1 and 2. A central feature of their approach was the repeated application of the inherently chiral secondary organometallic reagent 5. The first use of 5 was the addition to the aldehyde 4. The product 6 was ozonized, and the resulting aldehyde was carried on to the α, β-unsaturated ester. Exposure of the hydroxy ester to benzaldehyde under basic conditions delivered, by intramolecular Michael addition, the acetal 7. The next addition of the reagent 5 was to the aldehyde 10. The adduct 11 was deprotonated with t-BuLi to effect α-elimination, providing, after protection of the alcohol, the alkyne 12. Coupling of 12 with the amide 7 gave a ketone, enantioselective reduction of which under Itsuno-Corey conditions led, again after protection of the alcohol, to the alkyne 13. Oxidation followed by selective hydrogenation and iodine-tin exchange then completed the assembly of 1. Note that PtO2, not typically used for partial hydrogenation, was the catalyst of choice for this congested alkyne. The third application of the enantiomerically-pure reagent 5 was addition to the aldehyde that had been prepared by ozonolysis of 15. Advantage was then taken of another property of the alkenyl carbamate, Ni-mediated Grignard coupling, to form the next carbon-carbon bond with high geometric control. Deprotection of the diene 17 so prepared followed by iodination then completed the synthesis of 2. The convergent coupling of 1 with 2 was carried out under Suzuki conditions. Reduction of the iodide of 2 to the corresponding alkyl lithium followed by exchange with B-OMe-9-BBN gave an intermediate organoborane, that smoothly coupled with 1 under Pd catalysis to give 18.