TY - JOUR
T1 - Conformational Analysis of 1,3-Dioxanes with Sulfide, Sulfoxide, and Sulfone Substitution at C(5). Finding an Eclipsed Conformation in cis-2-tert-Butyl-5-(tert-butylsulfonyl)-l,3-dioxane
AU - Juaristi, Eusebio
AU - Martinez, Roberto
AU - Mendez, Rodolfo
AU - Toscano, Ruben A.
AU - Glass, Richard S.
AU - Petsom, Amorn
AU - Eliel, Ernest L.
AU - Soriano-garcia, Manuel
PY - 1987/8/1
Y1 - 1987/8/1
N2 - The positions of equilibrium, established by acid catalysis, between diastereomeric cis- and trans-5-(tert-butylthio)-(1), 5-(tert-butylsulfiny1)- (2), and 5-(tert-butylsulfonyl)-2-isopropyl-l,3-dioxanes (3) are reported and compared with previously published data for the 5-methylthio (4), 5-methylsulfinyl (5), and 5-methylsulfonyl (6) analogues. Although AG° values for the sulfides 1 and 4 are very similar, the difference in conformational behavior for sulfoxides 2 and 5 is significant, and the effect of changing from methyl to tert-butyl in the sulfones (6 — 3) is quite dramatic: the large preference of the methyl analogue for the axial position (1.19 kcal/mol) is reversed in 3 where the equatorial isomer is more stable by 1.14 kcal/mol. The conformational behavior in 1–6 is discussed in terms of the rotamer population of the axial isomer, in which steric and electrostatic effects are dominant. X-ray crystallographic data on cis-2-tert-butyl-5-(tert-butylsulfonyl)-l,3-dioxane (cis-9 axial sulfonyl) show that the SS-£er£-butyl group is outside the ring, with both sulfonyl oxygens above the dioxane ring and eclipsing the endocyclic C-C bonds. The electrochemical behavior of cis-1 and trans-1 supports the idea that lone-pair/lone-pair electron repulsion is responsible for the large predominance of the equatorial isomer.
AB - The positions of equilibrium, established by acid catalysis, between diastereomeric cis- and trans-5-(tert-butylthio)-(1), 5-(tert-butylsulfiny1)- (2), and 5-(tert-butylsulfonyl)-2-isopropyl-l,3-dioxanes (3) are reported and compared with previously published data for the 5-methylthio (4), 5-methylsulfinyl (5), and 5-methylsulfonyl (6) analogues. Although AG° values for the sulfides 1 and 4 are very similar, the difference in conformational behavior for sulfoxides 2 and 5 is significant, and the effect of changing from methyl to tert-butyl in the sulfones (6 — 3) is quite dramatic: the large preference of the methyl analogue for the axial position (1.19 kcal/mol) is reversed in 3 where the equatorial isomer is more stable by 1.14 kcal/mol. The conformational behavior in 1–6 is discussed in terms of the rotamer population of the axial isomer, in which steric and electrostatic effects are dominant. X-ray crystallographic data on cis-2-tert-butyl-5-(tert-butylsulfonyl)-l,3-dioxane (cis-9 axial sulfonyl) show that the SS-£er£-butyl group is outside the ring, with both sulfonyl oxygens above the dioxane ring and eclipsing the endocyclic C-C bonds. The electrochemical behavior of cis-1 and trans-1 supports the idea that lone-pair/lone-pair electron repulsion is responsible for the large predominance of the equatorial isomer.
UR - http://www.scopus.com/inward/record.url?scp=0001274423&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0001274423&partnerID=8YFLogxK
U2 - 10.1021/jo00226a015
DO - 10.1021/jo00226a015
M3 - Article
AN - SCOPUS:0001274423
SN - 0022-3263
VL - 52
SP - 3806
EP - 3811
JO - Journal of Organic Chemistry
JF - Journal of Organic Chemistry
IS - 17
ER -