D. A. Evans [2, 31-Sigmatropic Rearrangements: An Introduction Chem 206 [2, 3]Sigmatropic Rearrangements The basic process MeMe temp R2 R2 X—Y Rautenstrauch. Chem Commun. 1979.1970-25C-70% X&Y=permutations of C, N,o, s, Se, P; however X is usually a heteroatom X-S, Y=C; Sulfonium Ylide Rearrangement Attributes: Stereoselective olefin construction chirality transfer Representative X-Y Pairs N-o(amine oxides) S-P, S-N, S-o(sulfoxides S-C(sulfur ylids) o-P(phosphites O-C(Wittig rearrangement) N-N, Cr-C (haloium ylids N-c(nitrogen ylid P-C, C-C (homoallylic anions) ythgoe, Chem Commum 1972, 757 S-s(disulfides) ■X·NY=c; Ammonium Ylide Rearrangement An important early paper: Baldwin, J. Chem. Soc., Chem. Comm. 1970, 576 o Sommelet-Hauser: ■ General reviews: Trost, Ed, Comprehensive Organic Synthesis 1992, Vol 6, Chapter 4.6 Nakai, T: Mikami, K Org. React (N.Y. )1994, 46, 105-209 Hoffmann, Angew. Chem. Int Ed. 1979, 18, 563-572 (Stereochemistry of Nakai, Chem. Rev. 1986, 86, 885-902 Wittig Rearrangement Evans, Accts. Chem. Res. 1974, 7, 147-55(sulfoxide Rearrangement) Vedejs, Accts. Chem. Res. 1984. 17, 358-364 (Sulfur Ylilde Rearrangements) IX-0, Y=C; Wittig Rearrangement Review, Pines, Org. Rxns 1970, 18, 416 23] o Modern versions of stevens: R2 Me2N CN Garst, JACS 1976, 98, 1526 Mander JoC 1973. 38. 2915N Me CN Me R2 R1 R3 – + X Y: R2 R R3 Me O Ph Me Ph O R BuLi BuLi R O Ph Li+ Me Ph O Me Li+ R2 R R3 :X Y Ph O H Li R• Me LiO Ph Me Y :X R R3 R2 Li O R Ph N Me Me Me N R1 R3 R2 Me CN Me O Me Me Me Me S S BuLi BuLi BuLi BuLi N CH2 Me Me O Me Me Me Me S S Li+ CH2 NMe2 H OH Me Me Me Me Me2N R1 R3 R2 CN S S OH Me Me Me Me Me NMe2 important extension lacking CN FG; Sato, JACS 1990, 112, 1999 Mander, JOC 1973, 38, 2915 Buchi, JACS 1974, 96, 7573 + ■ X - N, Y = C; Ammonium Ylide Rearrangement: – ■ X - S, Y = C; Sulfonium Ylide Rearrangement: Lythgoe, Chem Commum 1972, 757 D. A. Evans [2,3]-Sigmatropic Rearrangements: An Introduction Chem 206 – ❐ Sommelet-Hauser: [2,3] ❐ Modern versions of Stevens: Review, Pines, Org. Rxns 1970, 18, 416 [2,3] [2,3] [2,3] Sigmatropic Rearrangements ✻ ✻ ■ General Reviews: ■ Representative X-Y Pairs: ‡ An important early paper: Baldwin, J. Chem. Soc., Chem. Comm. 1970, 576 S–P, S–N, S–O (sulfoxides) O–P (phosphites) N–N, Cl+–C (haloium ylids) P–C, C–C (homoallylic anions). Attributes: Stereoselective olefin construction & chirality transfer ■ The basic process: X & Y = permutations of C, N, O, S, Se, P; however X is usually a heteroatom Trost, Ed., Comprehensive Organic Synthesis 1992, Vol 6, Chapter 4.6: Nakai, T.; Mikami, K. Org. React. (N.Y.) 1994, 46, 105-209. Hoffmann, Angew. Chem. Int. Ed. 1979, 18, 563-572 (Stereochemistry of) Nakai, Chem. Rev. 1986, 86, 885-902 (Wittig Rearrangement) Evans, Accts. Chem. Res. 1974, 7, 147-55 (sulfoxide Rearrangement) Vedejs, Accts. Chem. Res. 1984, 17, 358-364 (Sulfur Ylilde Rearrangements) N–O (amine oxides) S–C (sulfur ylids) O–C (Wittig rearrangement) N–C (nitrogen ylids) S–S (disulfides) Baldwin, JACS 1971, 93, 3556 – ■ X - O, Y = C; Wittig Rearrangement: [2,3] – [1,2] • Garst, JACS 1976, 98, 1526 base temp Rautenstrauch, Chem Commun. 1979, 1970 –25 °C ~70% ~30%