Internally versus externally solvated derivatives of doubly bridged 1,4-dilithio-2-butene: structures and dynamic behavior. A "T" shaped dimeric cluster in the solid state

X-ray crystallographic NMR and calculational modeling studies using B3LYP/6-311G* of selected dilithium derivatives of the 1,3-butadiene dianion including cis-dilithio-1,4-bis(TMS)-2-butene·(TMEDA)(2)2, internally solvated cis-dilithio-1,4-bis[bis(2-methoxyethyl)aminomethyldimethylsilyl]-2-butene 5, and using only modeling, 1,4-dilithio-2-butene·(TMEDA)(2)9 reveal remarkably similar structural and NMR parameters. In the solid, 5 consists of unusual "T" shaped dynamic clusters. In all three bridging lithiums are sited between 1.8 and 1.9 Å normal to the centroids of opposite faces of the near coplanar of the 2-butene component. Typical bond lengths of the latter are 1.458 ± 0.004, 1.385 ± 0.006, and 1.459 ± 0.003 Å, for C1-C2, C2-C3, and C3-C4, respectively. The (13)C chemical shifts lie within the ranges δ 21 ± 0.5, 99 ± 0.7, 99 ± 0.7 and 21 ± 0.5 for C1, C2 and C3 together, and C4, respectively. Dynamic (13)C NMR provides activation parameters for nitrogen inversion in 2 and 5, overall molecular inversion of 5, and conformational interconversion of 2.

Hormonal control of eclosion of flies from the puparium

Pharate flies (Sarcophaga bullata) very close to eclosion were injected with hemolymph from eclosing flies or various other preparations, kept at 10 degrees C for 24 hr, returned to room temperature, and tested for eclosion behavior (ongoing, attempted, or completed eclosion) during the first 30 min, the subsequent 2(1/2) hr, and after 51 hr. Flies injected with "eclosion" hemolymph showed significantly more eclosion activity during the first 30 min than noninjected controls, flies injected with hemolymph from larvae, or flies injected with Ringer solution.

Puparium formation in flies: contraction to puparium induced by ecdysone

Larvae of the fly Calliphora erythrocephala (Meigen) were deprived surgically of their ring glands at an age prior to the appearance of ecdysone in the blood, and then injected with ecdysone. They contracted into the typical barrel-shaped puparium, before the onset of tanning. This proved that ecdysone controls the puparium contraction as well as tanning.

Correlated effects of ecdysone and neurosecretion in puparium formation (pupariation) of flies

A neurohormone accelerates the formation and tanning of the fly puparium in the presence of ecdysone. When larvae of Phormia regina are divided by ligation into two parts before the critical period, the hind part remains untanned, unless injected with blood from a pupariating larva. This confirms earlier observations and is in contrast to recent data with another genus. When Sarcophaga bullata larvae are ligated after the critical period, the anterior part starts to tan about two hours before the posterior part. Injecting neurosecretory material from the brain, the pars intercerebralis, or the corpora cardiaca of S. bullata, or from the brain or c. cardiaca of Periplaneta or Pyrrhocoris into the posterior part induces it to tan before the anterior part. Injection of the same material into normal larvae after the critical period similarly accelerates puparium formation and onset of tanning. Injection of ecdysone or ecdysterone does not have these effects. Thus, the neurosecretory material does not act by causing the release of ecdysone from the ring gland and its function is different from that of the classical brain ("activating") hormone. When injected before the critical period together with ecdysone it potentiates the effect of ecdysone. It is suggested that its biological significance is to coordinate puparial contraction and tanning.

Role of ecdysone, pupariation factors, and cyclic AMP in formation and tanning of the puparium of the fleshfly Sarcophaga bullata

Two pupariation factors, anterior retraction factor (ARF) and puparium tanning factor (PTF), are absent from the hemolymph of larvae at the time of tanning accelerated by ARF/PTF, cyclic AMP, or dopamine. ARF and PTF are not involved in derepression of dopa decarboxylase (aromatic L-amino-acid decarboxylase, aromatic L-amino-acid carboxy-lyase, EC 4.1.1.28) synthesis initiated by ecdysone. Tanning is entirely inhibited by injection of two transcriptional inhibitors, actinomycin and BrdUrd, and two translational inhibitors, puromycin and cycloheximide. Retraction activity is more severely inhibited by the transcriptional than by the translational inhibitors. A tanning response is initiated by cyclic AMP in the presence of the transcriptional but not the translational inhibitors. Dihydric tanning substances (dopa, dopamine) initiate tanning in the presence of both types of inhibitors. Release of ARF and PTF from the central nervous system is inhibited by the four inhibitors. ARF totally reverses the inhibitory effects on retraction, whereas PTF does not reverse inhibition of tanning. These data are interpreted to mean that PTF is concerned with the regulation of two components of the tanning response: (i) acceleration of synthesis of a particular protein (associated with the tyrosine hydroxylation complex), and (ii) activation via cyclic AMP of a component of the tyrosine hydroxylating system.

Overt and covert effects of endogenous and exogenous ecdysone in puparium formation of flies

Mature larvae of Sarcophaga argyrostoma fail to form puparia when kept in contact with water, but pupariate after having been subsequently exposed to dryness for 30 hr. They become increasingly more sensitive to injected ecdysone the longer the exposure to dry conditions. A second wet treatment halts the production of hormone that had occurred during the dry period, and reduces a sensitization to injected ecdysone during the intervening dry treatment. Apparently, injected ecdysone had cumulative effects not with the endogenous or exogenous hormone, but with its covert effects which had arisen during the dry period and persisted throughout the second wet period. The hind parts of larvae ligated at the end of a wet period pupariate when injected with either one massive dose of ecdysone, or a far smaller total of several subsequent doses. In the case of two unequal doses, the effect was greater when the smaller dose was injected first. In order to get pupariation with minimal effective doses, a continuous supply of the hormone during a certain period is required. It is suggested that the inhibition of pupariation by moisture has arisen as an adaptation to unfavorable conditions.

Arylallylic lithium compounds, internally versus externally coordinated: comparison of their structures and dynamic behavior via X-ray crystallography and NMR

A comparison of externally coordinated arylallyllithiums with internally coordinated arylallyllithiums using a combination of X-ray and NMR studies shows that 2-bis(2-methoxyethyl)aminomethyl-1-phenylallyllithium 7, and 2-bis(2-methoxyethyl)aminomethyl-1,3-diphenylallyllithi um 8, are indeed fully internally coordinated with all phenyls endo, and lithium is close to one terminal allyl carbon. By contrast, among the externally coordinated analogs 1-phenylallyl-lithium.(HMPT)4 5, and 1-phenylallyllithium.(THF) 6, both phenyls are exo and the proximity of lithium to anion was only detected in compound 6. Lithium-7 NMR clearly identifies the Li(HMPT)4+ complex in 5, whereas a 7Li{1H} HOESY experiment reveals 7Li to be coordinated to THF in 6 and close to the PhC terminal allyl carbon. Carbon-13 NMR shows that all of the above compounds are fully delocalized despite differences among the sites of lithium and their separations from the anions. Changes in the 13C NMR line shapes show that the diphenyl compound 8 undergoes a very fast 1,3-lithium sigmatropic shift, and all of the phenyls in the above compounds undergo fast rotation around their phenyl Cipso-Callyl bonds. Barriers to rotation, DeltaH from NMR line shapes for 5, 6, 7, and 8 respectively, are 19.8, 14.6, 10.2, and 8.9 kcal x mol-1. The decrease in barriers is clearly correlated with a decrease in separation of lithium from an allyl terminal carbon and implies that especially among the latter three, 6, 7, and 8, lithium is involved in the mechanism for phenyl rotation. This question is discussed.

Structural distortions and dynamic behavior of the elusive "L"-shaped cis-bicyclo[3.3.0]octenyllithium: X-ray crystallographic and NMR studies

Substituted cis-bicyclo[3.3.0]octenyllithium prepared by addition of t-BuLi to 3-methylene-1,4-cyclooctadiene in the presence of TMEDA crystallizes as a dimer with one unsolvated Li(+) sandwiched between the external faces of two allyl anions in a triple ion, and external to it the second Li(+) is bidentately complexed to TMEDA, 8. Within each allyl unit, the allyl bonds have different lengths, and all four rings deviate from coplanarity which relieves strain in the rings despite introducing partial localization of the allyl anions. A similar structure prevails in solution as shown by (7)Li NMR and the results of (7)Li{(1)H} HOESY and (1)H, (1)H NOESY experiments. Carbon-13 NMR line shape changes indicate that the system undergoes a fast allyl bond shift concerted with conformation shifts of the out of plane carbons, ca. DeltaG = 9 kcal x mol(-1). Cyclopentyllithium prepared by CH(3)Li cleavage of the trimethylstannyl derivative slowly undergoes an allowed ring opening to pentadienyllithium as well as deprotonating the solvent. The different behavior of dienylic lithium species is attributed to the relative separation of their termini.

Perturbation of Conjugation in Internally Solvated Allylic Lithium Compounds: Variation of Ligand Structure. NMR and X-ray Crystallography

Several allyic lithium compounds were prepared with different potential ligands tethered at C2. These are with CH3OCH2CH2NCH3CH2-, 5 and 1-TMS 6, with (CH3)2NCH2CH2NCH3CH2-, 1-TMS 7, and with ((CH3)2NCH2CH2)2NCH2-, 8 and 1-TMS 9. In all these compounds Li is fully coordinated to the pendant ligand and is sited off the axis perpendicular to the allyl plane at one of the allyl termini as indicated by a combination of X-ray crystallography and NMR spectra. Compounds 5 and 8 are Li-bridged dimers as shown by X-ray crystallography and also dimeric in benzene solution as determined from freezing point determinations. Compounds 6, 7, and 9 are monomeric in THF-d8 or diethyl ether-d10 solution and exhibit one bond 13C1, 6Li scalar coupling at low temperature. Taken together the crystallographic and NMR data indicate that all of these compounds incorporate partially delocalized allylic moieties. Compounds 5 and 8 undergo fast 1,3-Li-sigmatropic shifts that are proposed to take place within low concentrations of monomers in fast equilibrium with prevalent dimers. Averaging with increasing temperature of the one-bond 13C, 6Li coupling constant in 6, 7, and 13 provided the dynamics of bimolecular C-Li exchange with Delta H++ values of 6.7, 12, and 13 kcal x mol(-1), respectively. Averaging of the diastereotopic N(CH3)2 13C resonances of 7 is indicative of fast transfer of coordinated ligand between faces of the allyl plane Delta H++ = 5.3 kcal x mol(-1) combined with slower inversion at nitrogen. Compound 8 exhibits similar effects. It is concluded that variation of the ligand structure changes dynamic behavior of the compounds but has little influence of their degrees of delocalization.

Internally solvated cyclopentadienyllithium compounds: structural integrity of the Cp-Li+ moiety. NMR, dynamics, X-ray crystallography, and calculations

[Structure: see text]. N(CH2CH2OCH3)2 are as follows: T = CHCH(CH3)2, 6; T = (CH2)2, 10; T = (CH2)3, 14. The results of NOE NMR experiments for 6, 10, and 14 together with X-ray crystallography of 14 support internally coordinated monomeric structures for all three compounds. Models have been constructed for 6, 10, and 14 from modifications of an internally solvated allylic lithium compound at the B3LYP level of theory using basis set 6-311G*. The resulting structural features are very similar to those obtained from the NMR and crystallographic data. In addition, 13C NMR shifts obtained with the GIAO procedure using the results of the B3LYP/6-311G* calculations are closely similar to the experimental shifts, which validate B3LYP as a suitable model for these compounds. The Li+ centroid distance of ca. 1.9 A to 2.0 A obtained for 6, 10, and 14 is common to most crystallographic data for externally solvated Cp-Li+ compounds as well as one which incorporates a (CpLiCp)- triple ion. It is concluded that the ligand tether and the stereochemistry around Li+ accommodate to maintain the structural integrity of Cp-Li+. NMR and crystallography show 14 to be chiral. Carbon-13 NMR line shape changes are attributed to inversion via a lateral wobble mechanism with DeltaH++ = 6 kcal x mol(-1) and DeltaS++ = -2 eu. It is also shown that a 6,6-dimethylfulvene is deprotonated at methyl by LiN(CH2CH2OCH3)3 as well as by butyllithium in the presence of PMDTA producing isopropenyl Cp-Li+ compounds 24 and 25, respectively. NMR line shape changes of the sample containing 24 have been qualitatively interpreted to result from a combination of fast transfer of coordinated ligand between faces of the carbanion plane as well as a lithium-exchange process.

NMR Studies of Structure and Reorganization Dynamics of an [6Li]-Allylic Lithium Compound Complexed to [14N,15N]-N,N,N‘,N‘-Tetramethylethylenediamine: Inversion and Ligand Lithium Exchange

Proton, 13C, 6Li, and 15N NMR line-shape studies of exo,exo-1-trimethylsilyl-3-(dimethylethylsilyl)allyllithium-6Li complexed to [14N,15N]-N,N,N',N'-tetramethylethylenediamine (TMEDA) 2 as a function of temperature and of added diamine reveal the dynamics of three fast equilibrium reorganization processes. These are (with DeltaH values in kilocalories per mole and DeltaS values in entropic units): mutual exchange of lithium between two 2 molecules (6.3, -21), exchange of TMEDA between its free and complexed states (5.0 and -22), and first-order transfer of complexed ligand between the allyl faces (7.0 and -20). Intermediates that are dimeric in TMEDA are proposed for the first two of these reorganization processes.

Perturbation of Conjugation in Allylic Lithium Compounds Due to Stereochemical Control of Internal Lithium Coordination: Crystallography, NMR, and Calculational Studies

Several allylic lithium compounds have been prepared with ligands tethered at C(2). These are with (CH(3)OCH(2)CH(2))(2)NCH(2)-, 6, 1-TMS 5, 1,3-bis(TMS) 8, and 1,1,3-tris(TMS) 9. Allylic lithiums with (CH(3)OCH(2)CH(2))(2)NCH(2)C(CH(3))(2)-, are 10, 1-TMS 11, and 1,3-bis(TMS), 12 compounds with -C(CH(3))(2)CH(2)N-((S)-(2-methoxymethyl)-pyrrolidino) at C(2) 13, 1-TMS 14, and 1,3-bis(TMS) 15. In the solid state, 8-10 and 12 are monomers, 6 and 13 are Li-bridged dimers, and 5 and 7 are polymers. In solution (NMR data), 5, 7-12, 14, and 15 are monmeric, and 6 is a dimer. All samples show lithium to be closest to one of the terminal allyl carbons in the crystal structures and to exhibit one-bond (13)C-(7)Li or (13)C(1)-(7)Li spin coupling, for the former typically ca. 3 Hz and for the latter 6-8 Hz. In every structure, the C(1)-C(2) allyl bond is longer than the C(2)-C(3) bond, and both lie between those for solvated delocalized and unsolvated localized allylic lithium compounds, respectively, as is also the case for the terminal allyl (13)C NMR shifts. Lithium lies 40-70 degrees off the axis perpendicular to the allyl plane at C(1). These effects are variable, so the trend is that the differences between the C(1)-C(2) and C(2)-C(3) bond lengths, (13)delta(3)-(13)delta(1) values, and the (13)C(1)-(7)Li or (13)C-(6)Li coupling constants all increase with decreasing values of the torsional angle that C(1)-Li makes with respect to the allyl plane.

Axial chirality in 1,4-disubstituted (ZZ)-1,3-dienes. Surprisingly low energies of activation for the enantiomerization in synthetically useful fluxional molecules

Trialkylsilyltrialkylstannes (R(3)Si-SnR'(3)) add to 1,6-diynes in the presence of Pd(0) and tris-pentaflurophenylphosphine to give 1,2-dialkylidenecyclopentanes with terminal silicon and tin substituents. The (ZZ)-geometry of these s-cis-1,3-dienes, resulting from the organometallic reaction mechanisms involved, forces the silicon and tin groups to be nonplanar, thus making the molecules axially chiral. There is rapid equilibration between the two helical forms at room-temperature irrespective of the size of the Si and Sn substituents. However, the two forms can be observed by 1H, 13C, and 119Sn NMR spectroscopy at low temperature. The rates of enantiomerization, which depend on the Si and Sn substituents, and the substitution pattern of the cylopentane ring can be studied by dynamic NMR spectroscopy using line shape analysis. The surprisingly low energies of activation (DeltaG++ = 52-57 kJ mol(-1)) for even the bulky Si and Sn derivatives may be attributed to a widening of the exo-cyclic bond-angles of the diene carbons.

Dynamic helical chirality of an intramolecularly hydrogen-bonded bisoxazoline

The synthesis and conformational properties of 2,6-bis-[2-((4S)-4-methyl-4,5-dihydro-1,3-oxazol-2-yl)phenyl]carbam oylpyridines, 2, have been described. Bisoxazoline 2a was prepared in five steps from 2-nitrobenzoyl chloride in an overall yield of 71%. In contrast to related structures such as 1, bisoxazoline 2a exhibits a highly biased P-type helical conformation in solution and in the solid state. In the crystal lattice, 2a further assembles into a left-handed helical superstructure aligned along the crystallographic c axis. The barrier to helical interconversion, as measured by line-shape analysis of the temperature-dependent (1)H NMR spectra of thiobenzyl derivative 2b, was determined to be quite low ((Delta)G(++) = 12.3 kcal/mol), indicating the presence of a highly dynamic helical chirality.