Stereoselective synthesis and stereochemistry of r-2-alkoxycarbonyl-c-3-o-substituted phenyl-1,4-thiazane 1,1-dioxides

r-2-Alkoxycarbonyl-c-3-aryl-1,4-thiazane 1,1-dioxides were obtained as the stereoselective product, when the aldehyde used was o-substituted benzaldehyde while the p-substituted benzaldehydes gave a trans product. The relative configuration of the adjacent alkoxycarbonyl and aryl groups was assigned from the vicinal coupling constant, 3J = 10.6 Hz in the trans isomer and 3.2 Hz in the cis isomer, and from the multiplicity pattern, i.e., a doublet for the H-2 proton of the trans isomer and a triplet for the H-2 proton of the cis isomer. The unusual, large long-range coupling (4J = 2.8 Hz) because of the "W" arrangement between H-2e and H-6e across the ring type was very useful for confirming the cis configuration and chair conformation of the isomer. The various 1H and 13C NMR assignments were made with the help of 1H–1H COSY, 1H–13C COSY, HMBC, and NOESY spectral analyses.Key words: 1H and 13C NMR, 1H–1H COSY, 1H–13C COSY, HMBC, NOESY, stereoselectivity, 1,4-thiazane.

Reaction of carbanions generated from arylmethylphosphonates with cyclic enones. Regio- and stereoselectivity of addition

α-Lithiated benzylphosphonate esters, XC6H4CH(Li)PO3Et2, add regioselectively to cyclohex-2-enone at the carbonyl group; higher reaction temperatures lead to the reversal to the starting materials, and not to the 1,4-addition. Relative configuration of the C(1) and Cα centers in the 1,2-adducts was determined from the 13C NMR spectra. For 2-methylcyclohex-2-enone the regioselectivity of the addition is decreased. The lithioderivative of diethyl 1-naphthylmethylphosphonate, C10H7CH(Li)PO3Et2, shows reverse regioselectivity yielding the 1,4-, but not the 1,2- addition product. The crystal and molecular structure of that 1,4-adduct has been determined and demonstrates that the conformation about the C(1)-Cα bond is close to that existing in solution, deduced from the value of the 1H NMR 3JHH vicinal coupling constant of the H(1)-C(1)-Cα-H hydrogens. The same conformation was also confirmed as the most stable by molecular modeling. Key words: α-lithiated arylmethylphosphonates, 1,2- vs. 1,4-addition to cyclic enones, steric effects of the cyclohex-2-enone, molecular structure and molecular modelling of the 1,4-adduct of 1-naphthylmethylphosphonate to cyclohex-2-enone.

NMR Spectroscopic Studies of Thialene (Cyclopenta[b]thiapyran) and Isothialene (Cyclopenta[c]thiapyran)

1H and 13C NMR spectral parameters are reported for the S-pseudoazulenes thialene (cyclopenta[b]thiapyran) (I) and isothialene (cyclopenta[c]thiapyran) (II). Both compounds display complex first order spectra, with thialene having 10 and isothialene 14 of 15 possible coupling constants. Complete unambiguous assignments of all protons and non-quaternary carbons were made via 2-dimensional NMR techniques and PPP-SCF π-electron density/chemical shift and π-bond order/vicinal coupling constant correlations.

An improved approach to benzene annelation: the synthesis of 11-substituted octahydro-1,4:9,10-dimethanoanthracenes and a study of OH…p bonding in these systems

A procedure for benzene annelation, which incorporates the best features of previously reported techniques, is described and is applied to the synthesis of a series of 11-substituted octahydro-1,4:9,10-dimethanoanthracenes (1a-e). Thus addition of 1,2,3,4-tetrachloro-5,5-dimethoxycyclopentadiene(7) to (1β,4β, 4aα, 5α, 8α, 8aα)-anti-9-acetoxy-1,2,3,4,4a,5,8,8a-octahydro-1,4:5,8-dimethanonaphthalene(4b) gave the adduct (8b).* Deacetalization of (8b) followed by thermal, cheletropic loss of CO and subsequent base-induced dehydrochlorination gave the 5,6,8-trichlorooctahydro-1,4:9,10-dimethanoanthracen-anti-11-ol (17b) which could easily be converted into (1c) by using sodium and ethanol. Infrared and 1H n.m.r. studies revealed the presence of a strong intramolecular OH…π bond in the syn-alcohol (1e). The observation of an unusually large vicinal coupling constant, J(HCOH) 12 Hz, for (1e) implies that the H-C-O-H exists in the antiperiplanar conformation which also maximizes the strength of the OH…π bond.

Long-range coupling and conformation in some thienylmethylene and furfurylidene derivatives

The p.m.r, spectra of 12 2-thienylmethylene and furfurylidene derivatives are reported. The average conformation about the Ar-CHXY bond is deduced from the magnitude of the meta (and ortho) long-range benzylic coupling constants. In thiophens, conformations in which the benzylic hydrogen is in or near the plane of the aromatic ring and anti to the ring sulphur are preferred. In furans the hydrogen-in-plane conformations are again favoured. The signs of the meta and ortho benzylic coupling constants have been determined and are positive and negative respectively with respect to the vicinal coupling constant J3,4.