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The thermal [C.sup.2]-[C.sup.6] cyclization of the enyne-allenes and their ring-closed and ring-opened products is described using an ultrafast radical clock. The results have provided a direct evidence for a stepwise mechanism in the [C.sup.2]-[C.sup.6] cyclization of enyne-allenes.

The pseudo-Jahn-Teller (PJT) interactions occurring between two low-lying Jahn-Teller (JT) doubly degenerate electronic states of the prototypical cyclopropane radical cation ([CP.sup.+]) are studied. The analysis reveals vibronic level spectra and the ultrafast nonradiative decay of the excited cationic states are related to the highly complex entanglement of electronic and nuclear degrees of freedom in the prototypical molecular system.

An ab initio study is performed for the singlet-triplet gap in trimethylenmethane (TMM) and of the ring-opening of methylenecyclopropane by the multireference BWCC method. A multireference method is used because the singlet states of TMM and intermediates between TMM and methylenecyclopropane have a strong multiconfigurational character.

A general and highly efficient asymmetric synthesis of potent and selective bicyclo[3.1.0]hexanes mGluR2/3 agonists is described. Densely functionalized, enantiomerically pure, monoprotected diols were prepared through a Et3Al-mediated intramolecular cyclopropanation with respect H or F endo selectivity in excellent yields.

A report that regioselective distal bond cleavage of methylenecyclopropanes is accomplished, irrespective of the structure of the substituent R(super 1), by using the cyclic amides. The selectivity of the respective ring-opening position depends on the substituents of methylenecyclopropanes.

Density functional theory calculations for the cyclopropanation reactions of several mono zinc carbenoids and their corresponding gem-dizinc carbenoids with ethylene are reported. Results indicate that gem-dizinc carbenoids react with C=C bonds with significantly lower barriers to reaction and in a noticeably different manner than Simmons-Smith type mono zinc carbenoids.

The gas-phase heat of formation (DeltaH (subf, 298)) of the 1,3,5-tridehydrobenzene triradical has been determined by using a negative ion thermochemical cycle. The trends in the first, second, and third bond dissociation energies of the benzene are similar to those found for cycloprophane, suggesting a cycloprophenyl-like electronic structure within the six-membered ring of the 1,3,5-benzene triradical.

Isothermal titration calorimetry and X-ray crystallography are used to determine the structural and thermodynamic consequences associated with constraining the pTyr residue of the pYEE Iigand for the Src homology two domain of the Src kinase. It is observed that drop in enthalpy with the conformationally constrained peptide mimic arises from sources other than changes in buried surface areas, though the exact origin of the differences remain unclear.

The UV-vis spectroscopy technique is employed to explain the mechanisms involved in the reactions of stabilized and semistabilized sulfur ylides with benzhydrylium ions. The various advantages and issues related to the application of sulfur ylides for the purpose of cyclopropanations are explained.

Quantitative evaluations of the aromaticity (antiaromaticity) of neutral exocyclic substituted cyclopropenes [(HC).sub.2]C=X (X = BH to InH), C[H.sub.2] to Sn[H.sub.2], NH to SbH are described. Electronegative X-based substituents are observed to increase the aromaticity of the cyclopropene rings, while electropositive substituents have the opposite effect.

An enantioselective desymmetrization of cyclopropenes by intermolecular Rh-catalyzed hydroacylation is described. The studies have shown that cyclopropylketones, bearing quaternary stereocenters, are produced with diastereocontrol and excellent enantiomeric excess.

Tetravinylbenzene is prepared in quantitative yield from tetrabromobenzene, where one-step procedure has used Suzuki-Miyaura cross-coupling conditions. Intramolecular cyclopropanation of monoadduct, putatively by its methyllithium-generated cyclopropylidene(oid) has produced a compound featuring a highly distorted spiropentane having a C-C-C bond angle.

Density functional theory (DFT) is used for examining the zinc carbenoid-mediated homologation reaction of [beta]-keto esters. Pathway B has explained the proposed, but spectroscopically unobservable donor-acceptor cyclopropane intermediate, while the second pathway A has disclosed an alternative to the classical intermediate in that a cyclopropane transition state leads to product.

The vibronic interaction in the [1.1.1]propellane radical cation has mixed the [super 2][A.sub.1]' ground state with the [super 2]E' first excited state that has resulted in the destabilization of a lateral C-C bond and the initial formation of the methylenebicyclobutyl radical cation. The studies have supported the Heilbronner-Wiberg interpretation of the vibrational structure in the photoelectron spectrum of [1.1.1]propellane in terms of vibronic coupling.

Cyclopropyl malonoyl peroxide, which is prepared in a single step from the diacid, is an effective reagent for the dihydroxylation of alkenes. The reaction has proceeded with syn selectivity with 1,2-disubstituted alkenes and a mechanism supported by oxygen-labeling studies is described.

Cu-TolBINAP-catalyzed conjugate addition of Grignard reagents to 4-chloro-[alpha],[beta]-unsaturated esters, thioesters, and ketones have led to 4-chloro-3-alkyl-substituted thioesters and ketones upon protonation of the corresponding enolates at low temperatures. Tandem conjugate addition-enolate trapping has produced trans-1-alkyl-2-substituted cyclopropanes, whose versatility is shown by the formation of key intermediates for the synthesis of cascarillic acid and grenadamide.

A facile synthesis of 2-carbamoyl-2-cyanocyclopropanecarboxylates through a tandem iodosobenzene/tetrabutylammonium iodide-induced oxidative cyclization and a subsequent neighboring group-assisted decarboxylation of the Michael adducts of 2-cyanoacetamides with [alpha],[beta]-unsaturated malonates is described. The method is observed to proceed smoothly under mild conditions and with good functional group tolerance and could be used to obtain highly functionalized cyclopropanes in moderate to good yields and with excellent diastereoselectivities.

The synthesis of a niobium cyclpropyl complex ([Tp.sup.Me2]NbMe(c-[C.sub.3][H.sub.5])(MeCCMe)) is described and has shown that thermal loss of methane from the compound has generated an intermediate that is capable of activating both aliphatic and aromatic C-H bonds. C-H activation chemistry of the type has represented an unusual reactivity pattern for [[eta].sup.2]-alkene complexes but is favored by the strain in the [C.sub.3] ring that has prevented the decomposition of the key intermediate via loss of cyclopropene.

Tandem methods are described for the catalytic asymmetric preparation of enantioenriched [beta]-hydroxy (E)-enamines and aminocyclopropanes. The diastereoselective hydrogenation of enantioenriched (E)-trisubstituted hydroxy enamines is described for generating 1,2-disubstituted-1,3-amino alcohols.

The t-BuCN-stabilized zirconacyclopropene-azasilacyclopentadiene complexes 2 are generated in situ in high yields from the Si-tethered diynes ([Cp.sub.2]Zr(II) species) and 2 equiv of t-BuCN through the coordination-induced Zr-C/Si-C bond cleavage and reorganization. t-BuCN has behaved as both an initiator and a brake/release handle to initiate and control the reaction process.

The synthesis of 1,2,10-tetrahydro-9H-cyclobuta[e]indol-4-one (CbBI), containing structural modification in the CC-1065 and duocarmycin alkylation subunit consisting of the incorporation of a ring-expanded fused cyclobutane, and its chemical and structural characterization and its incorporation into a key analogue of the natural products are described. The stability of N-Boc-CbBI relative to N-Boc-CBI containing a cyclopropane is attributed to the combination of the increased extent of vinylogous amide conjugation, the nonoptimal geometric alignment of the cyclobutane with the activating cyclohexadienone and the lower strain energy of a cyclobutane versus a cyclopropane.

The rapid synthesis of 3,3-pyrollidinyl-spirooxindole cores from cyclopropyl spirooxindoles and aldehydes, amines and sulfonamides is described. This method has used microwave heating to access a biologically privileged scaffold in an efficient route amenable to library population.

The Pd-catalyzed cross-coupling of aryl bromides or triflates and cyclopropylmagnesium bromide in the presence of substoichiometric amounts of zinc bromide has produced cyclopropyl arenes. The cross-coupling of other alkyl, cycloalkyl and aryl Grignard reagents with aryl bromides under the same conditions have produced the corresponding substituted arenes.

A research program is developed for achieving synthesis of tetrahydrofurans from cyclopropanes and C[double bond]O [pi] bonds. Asymmetric syntheses of (+)-polyanthellin A and (+)-virgatusin are achieved, which have depended upon cyclopropane/aldehyde annulation for construction of the core tetrahydrofurans.

The first example of a heavier group 14 element alkyne analogue (AgAr'GeGeAr')+Sb[F.sub.6].sup.-] prepared from the reaction between a digermyne Ar'GeGeAr' (Ar' = [C.sub.6][H.sub.3]-2,6-[([C.sub.6][H.sub.3]-2,6-[Pr'.sub.2]).sub.2]) and AgSb[F.sub.6] at -40 degree [Celsius] is reported. The obtained (AgAr'GeGeAr') analogue behaving as a [pi] donor to a transition metal is best described as a hybrid of a [pi]-complex and a [sigma]-metallacyclopropene structure.

A study was conducted to determine the intramolecular [super 13]C kinetic isotope effects for the ring-opening of cyclopropylcarbinyl radical over a broad temperature range. The results along with the curvature in the Arrhenius plot of the isotope effects support the predicted importance of heavy-atom tunneling in cyclopropylcarbinyl ring-opening.

The dirhodium catalyzed tandem cyclopropanation/Cope rearrangement between bicyclic dienes and siloxyvinyldiazoacetate to achieve enantiodivergent [4 + 3] cycloadditions is reported. The reaction which proceeds by a cyclopropanation followed by a Cope rearrangement of the resulting divinylcyclopropane could be applied for the synthesis of (+)-barekoxide and (-)-barekol.

The preparation of precursors to [pi]-conjugated cyclopropenium polymers is described along with the electronic properties of cyclopropenone polymers in their pristine states and after acidification. The increased contributions of cyclopropenium cation aromaticity have restricted the quinodal charge carriers because of the enengetically less favorable proposition of disrupting the local aromatic stabilization.

The mechanism of aldehyde [alpha]-oxyamination reaction is analyzed and the use of a validated cyclopropane-based radical-clock substrate has shown that carbon-oxygen bond formation has occurred through an enamine activation manifold. The studies have shown that complexation between TEMPO and a simple metal salt has led to electrophilic ionic reactivity.

The monomer derived from achiral 1-(aminoxy)cyclopropanecarboxylic acid (OAcc) and oligopeptides consisting of a chiral [alpha]-aminoxy acid and an achiral [alpha]-aminoxy acid like OAcc are prepared and their structures are analyzed. The studies have disclosed achiral aminoxy acid residues like the OAcc unit as a useful building block to be included into chiral aminoxy peptides to mimic chiral helix structure.

Both enantiomers of the DHFR inhibitor iclaprim (R)-1 and (S)-1 are prepared from the cyclopropyl homoallyl alcohols (R)-6 and (S)-6. The moderate enantioselectivity of the products (R)- and (S)-1 is related to the Mitsunobu reaction, which has not proceeded with complete inversion of configuration.

Alkylidenecyclopropanes is prepared from enantiomerically enriched cyclopropene derivatives with 99% stereotransfer. The protocol consists of the stereoselective reaction of Grignard reagents with 1-alkoxymethyl-3-hydroxymethylcyclopropenes and a stereospecific [1,3] carbon shift reaction.

The reaction of 3-cyclopropyl propargylic carboxylates with Au(I) and Au(III) catalysts have produced selectively 5-(E)-alkylidenecyclopentenyl acetates through [3,3]-sigmatropic rearrangement of the carboxylic moiety followed by cyclopropyl ring opening and cyclization. The experiments have provided evidence for an Au-promoted cyclopropyl ring opening/epimerization/ring closure in both cis- and trans-cyclopropyl settings, which has competed with the cyclization event, thus eroding the stereochemical information transfer.

Density functional theory calculations are used for studying the mechanism of rhodium(II)-catalyzed cyclopropanation reactions with ethyl bromo-, chloro-, and iododiazoacetate. The relative energies of the side-on trajectory transition states compared to the end-on trajectory transition states are affected by both the substrate alkene and the carbenoid substituents, which are used for predicting the stereochemical outcome of cyclopropanation reactions.

1,3-Dipolar cycloaddition reactions of VDCP-diesters with aromatic diazomethanes generated in situ from the aromatic aldehydes and tosylhydrazine mediated by base produce pyrazole derivatives under mild conditions. A plausible reaction mechanism is proposed based on the control experiments along with the discussion on the regioselectivity.

A comparative CASSCF/6-31G*-level computational study is conducted on the concerted [3,3] sigmatropic rearrangements of cis-1-iminyl-2-ketenylcyclopropane, cis-1-iminyl-2-propadienylcyclopropane, and cis-1-iminyl-2-keteniminylcyclopropane. The results of the calculations on the [3,3] sigmatropic rearrangements involving additional transition structures have shown the relative uniqueness of the pseudopericyclic one.

The interaction of a sulfamate ester derived metallonitrene with an allene has generated a versatile intermediate with 2-amidoallylcation-like reactivity. This is capable of rearranging to produce highly substituted iminocyclopropanes or acting as a novel dipolar species engaging external dipolarophiles.

Rhodium(I)-catalyzed cyclopropanation reactions to efficiently convert nitrogen-tethered 1,6-enynes to azabicyclo[4.1.0]heptenes are reported. Rhodium(I)-catalyzed tandem cycloisomerization and carbonylative [3+3+1] cycloaddition reactions of a cyclopropylenyne are also reported.

The preparation of a new phosphate carbenoid [(n-BuO).sub.2]P(O)OZn[CH.sub.2]I and its application in organozinc-mediated reactions is described. The application of obtained carbenoid in the chain extension of 1,3-diketones and [2,3]-sigmatropic rearrangement reactions is also described.

The conversion of cyclopropane-fused carbohydrates into oxepines is a good method for accessing diverse members of the septanoside family of carbohydrate mimetics. 2-Bromooxepines are obtained via silver(I)-promoted thermal ring expansion of a D-glucal-derived gem-dihalocyclopropanated sugar and cyclopropane ring cleavage under basic conditions has led to 2-C-branched pyranosides.

Functionalized arenes are prepared by chelation-controlled [3+3] cyclization/cyclopropane opening reactions of 1-trimethylsilyloxy-1,3-butadienes with benzyloxy- or methoxy-substituted 1,1-diacyclopropanes. Mixed chromanes-isochromanes are prepared by using 1,3-bis(silyloxy)-1,3-butadie nes containing a remote chloride group.

The [OsTp[([k.sup.1]-OCMe).sub.2]([P.sup.i][Pr.sub.3])]B[F.sub.4] [Tp = hydridotris(pyrazolyl)borate] complex promoted cleavage of both C([sp.sup.3)-C([sp.sup.2]) bonds of benzylidenecyclopropane and 3-phenylpropylidenecyclopropane to yield the complexes [OsTp(=C=CHR)([[eta].sup.2]-C[H.sub.2]=C[H.sub.2])([P.sup.i][Pr.sub.3])]B[F.sub.4] (R = Ph, C[H.sub.2]C[H.sub.2]Ph) is reported. The reaction process proceeded via metallacyclopropene intermediates stabilized by an ethylene chelation assistant to yield ethylene-Os-vinylidene species.

N-Sulfonyl 1,2,3-triazoles have formed rhodium(II) azavinyl carbenes, which has reacted with olefins to produce cyclopropanes with excellent diastereo- and enantioselectivity.

Ag(I)-catalyzed intramolecular reaction of monoarylmethylenecyclopropanes (MCPs) tethered with 1,1,3-triarylprop-2-yn-1-ols which provides diastereoselective access to polysubstituted allenylcyclobutanols is reported. The obtained Au(I)- catalyzed allenylcyclobutanols provide a wide range of bridged bicyclic compounds with a vinyl-substituted quaternary stereogenic center stereoselectively.

The enantioselective total synthesis of (-)-acylfulvene and (-)-irofulven which features metathesis reactions for the rapid assembly of the molecular framework of these antitumor agents is discussed. The application of an Evans Cu-catalyzed aldol addition reaction via a strained cyclopropyl ketenethioacetal and the final RCM/dehydrogenation sequence for the formation of (-)-acylfulvene and (-)-irofulven is also discussed.

Several studies are conducted to explain the development and the synthetic applications of the enantioselective formation of the 1, 1-dicarboxy diesters. The results demonstrate the presence of an excellent trans-d irecting ability in the amide group present in the cycloproponation reactions.