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Conformational equilibria in 1-, 3-, and 4-methyl-1,2,3,4-tetrahydroisoquinolines (THIQs) and the diastereomeric pairs of their 1,3- and 1,4-dimethyl homologs have been determined by measurement of H3/H4(trans) coupling constants and have been confirmed by molecular mechanics [MMP2(85)] calculations. The experimental −ΔG° values (a → e) for the monomethyl compounds (computed values in parentheses) in kcal mol-1 are Me-1, 0.56 (0.46); Me-3, 1.63 (1.53); and Me-4, −0.32 (−0.22). Agreement of experimental and calculated values is very good as is the additivity of values for the dimethyl compounds (Table 1). Values for the corresponding hydrochlorides are Me-1, 0.19 (−0.34); Me-3, l.15 (1.46); and Me-4, 0.35 (0.10) kcal mol-1. The less than satisfactory agreement of experimental with computed data here is probably due to neglect of solvation. The very small or negative ΔG° values for Me-1 and Me-4 were ascribed not only to the pseudoaxial (rather than axial) nature of Me(ax) and the absence of a syn-axial hyd...

Results of IR and 1 H, 13 C, and 31 P NMR studies of the anancomeric title compounds (2‐5) and compound 1 (Scheme 1) are analyzed to search for the existence of high-energy boat or twist-boat conformations in the equatorial epimers. While the difference in frequencies (Dm)P4O between the axial and equatorial compounds and 13 C NMR JPOCC and anti JPOCCH3 values suggest the participation of twist-boat conformations for the equatorial isomers, coupling constants in 1 H NMR JH4H5a or JH6H5a and JH4H5e or JH6H5e of the equatorial isomers 2e‐4e along with the lack of a large 3 JPH in 31 P NMR are consistent with predominant chair conformations. In addition, an X-ray structure of the equatorial 2-p-nitrophenoxy-2-oxo-cis-4,6-dimethyl-1,3,2dioxaphosphorinane (4e) showed that the molecule adopts a chair conformation with no severe ring flattening in the OPO region in the solid state. X-ray structures of trans-4 and trans-5 displayed chair conformations with mild ring flattening especially in the axial methyl region, presumably as a result of the steric

The position of conformational equilibria in 2- and 3-methyl-1,4-thiazanes and cis- and trans-2,3-dimethyl-1,4-thiazanes, their N-methyl derivatives, and several of the correSponding sulfoxides and sulfones have been measured. The ΔG o values for the methyl groups are generally in agreement with what one would expect on the basis of known conformational equilibria in methylthianes, methylpiperidines, and N-methylated homologs of the latter; however, the differences in ΔG o between the 2-methyl and N,2-dimethyl homologs are even larger than in the piperidine series

In contrast to simple esters, α-alkoxy, α-alkylthio, and α-dimethylamino esters react with lithiooxathiane 1-Li in good yield to give the corresponding α-functionalized 2-acetylhexahydro-4,4,7-trimethyl-4H-1,3-benzoxathiin 2. In some cases, mixtures of diastereomers (2,2') are obtained. The reaction has been extended to α-methoxy- and α-[(triisopropylsilyl)oxy]propanoyl and α-(methylthio)butanoyl homologs which have chiral centers at C(α)

The addition of methyl- and phenylmagnesium bromide and phenyllithium to 2-(methoxyacetyl)-, 2-[(tri-isopropylsiloxy)acetyl]-, and 2-[(methylthio)acetyl]hexahydro-4,4,7-trimethyl-4H-1,3-benzoxathiin and the corresponding 2'-methyl, 2'-(triisopropylsiloxy)propionyl, and 2'-(methylthio)butyryl homologs has been studied

The syntheses of the title 1,4-thiazanes (thiamorpholines) by reduction of the 5-oxa-1,4-thiazanes resulting from the lactamization of the appropriate acyclic phenyl derivatives of 5-amino-3-thiapentanoic acid are reported. The oxidation reactions at sulfur yielded the corresponding sulfoxides and sulfones. The stereochemistry of all these compounds was unequivocally established from their 1 H-NMR spectroscopic parameters

The asymmetric synthesis based on a chiral 1,3-oxathiane developed some years ago (ref. 1.4) has been applied (ref. 6 ) to an efficient synthesis of the sex attractant pheromone of the bark beetle hyelocoerus dermestoides L., (R)-2,3-dihydro-2,5-dimethyl-2-isopropylfuran (Scheme 1). This work raised the question as to whether the intermediacy of chelates in Cram's "chelate rule" (ref. 15) is real. This question was answered (ref. 23) in the affirmative by kinetic and stereochemical studies of the reaction C2H5COCH(R)CH3 + (CH3)2Mg. The rate of this bimolecular reaction was measured by rapid injection nmr (ref. 24) and it was found for a variety of R's [OS~(~FY)~,OS~(C~H~)~~-BU, OSiMe2t-Bu, OSiEtj, OSiMej, OCH3J that stereoselectivity parallels rate qualitatively and quantitatively, with the non-chelating (ref. 17) OSi(iFr)g derivative reacting slowest (and at the same rate as propiophenone, R = H) and the chelating OCH3 compound reacting ca. 2000 times faster. The results are interpreted in terms of a competition between a non-chelating and a highly organized chelating transition state, with the R=OCH3 compound which chelates extensively reacting fastest and with over 99% stereoselectivity giving the Cram product. Some years ago we developed a method of enantioselective synthesis of tertiary (ref. 1) and secondary (ref. 2) hydroxyaldehydes, RRC(0H)CHO (R = alkyl or H) which have served as synthons for a variety of chiral, nearly enantiomerically pure target molecules. The chiral auxiliary in this method is the oxathiane 1 derived from naturally occurring enantiomencally pure (+)-pulegone (Scheme 1) (ref. 3). Two earlier reviews (ref. 4) as well as a number of more recent publications (ref. 5) have dealt with this synthesis. Scheme 1 SCH2CeHS Na, CH,W N-l3 6 I YE?& I 80-82% (+) P u leg on e (major isomer) I I I I I (Crystallizes; overall yield of crystalline product: 25%) (major isomer)

Previously studied highly stereoselective additions of Grignard, organolithium, and hydride reagents to the 2-benzoyl derivative of compound 1a have been extended to other 2-alkanoyl derivatives (1,R'=methyl, ethyl, isopropyl) and to the 2-benzoyl derivative with R=methyl. High diastereoselectivity is attained in most of the products

This editorial is based on talks one of us (ELE) gave in Canada, in the USA, in Argentina and in Chile. We realize that not everything said here will apply to all four countries; readers will have to take their pick

La lithiation du perhydro-4,4,7-trimethyl-«1,3»-benzooxatkine [A] suivie d'une reaction avec un nitrile puis d'une hydrolyse conduit a des 2-acyl [A]

In the context of a brief discussion of the career of Louis Pasteur (who died 100 years ago), the applications of »Pasteurian Resolutions" to modern sterochemistry, especially in its industrial applications, will be presented.

When I immigrated to this country some 50 years ago, a mentor told me, "As an immigrant, you must work three times as hard as a native to succeed." Other immigrants must have received that same message. Hard work, plus the enterprising spirit one needs to leave one's home country to deal with a new culture and often a new language, plus, in many cases, a better education, are perhaps the reasons that so many immigrant scientists have made good. Thus, 23% of the members of the National Academy of Sciences are foreign born, as are 23% of U.S. Nobel Laureates in chemistry since World War II. The percentage in physiology or medicine is 35%. And the contribution of foreign-born scientists, such as Enrico Fermi, Hans Bethe, and Eugene Wigner, in helping the U.S. to win World War II is legend. Stopping the immigration of scientists—including outstanding Ph.D.-degree graduates of U.S. universities— is surely counterindicated. ...

Etude par diffraction RX des structures cristallines des dimethyl-3,4 phenyl-4 cyclohexanone; phenyl-1 methyl-1 nitrobenzoyloxy-2 cyclohexane et methyl-4 phenyl-1 cyclohexanol

The barriers to phenyl rotation in 2-lithio-2-phenyl-cis-4,6-dimethyl-, 2-lithio-2-phenyl-4,4,6-trimethyl- and 2-lithio-2-phenyl-trans-4,6-dimethyl-1,3-dithiane are compared in tetrahydrofuran (THF) and hexamethylphosphortriamide (HMPA). In the first two cases, the barriers in THF are lower than those in HMPA, presumably because the lithio compound exists as a tight ion pair in THF but as a solvent-separated ion pair (with more delocalization of charge into the phenyl ring) in HMPA. However, in the trans-4,6-dimethyl compound the barriers are the same in the two solvents and nearly equal to the barriers for ring reversal. It is concluded that in this compound the rate-determining step for phenyl rotation may actually be ring reversal, at least in solvent HMPA.

Synthese a partir de benzyloxy-2 dodecanal via l'addition de bromure de pentene-4yl magnesium

(+)- and (−)-Frontalin have been obtained from a chiral 1,3-oxathiane precursor in a short (3-step) synthesis in moderate (70%) enantiomeric excess (e.e.). A longer (6-step) modification gives the ...