Reactions of Arylaldehydes and N-Sulfonated Imines with Dimethyl Acetylenedicarboxylate Catalyzed by Nitrogen and Phosphine Lewis Bases

Synthesis of new stable crystalline zwitterionic products from the reactions of 1-methylimidazole, acetylenic esters and strong cyclic CH-acids

The reactive 1:1 intermediate produced in the reaction between 1-methyl imidazole and dialkyl acetylenedicarboxylates was trapped by strong cyclic CH-acids such as N,N′-dimethylbarbituric acid, Meldrum's acid, cyclohexan-1, 3-dione, indan-1,3-dione, cyclopentan-1,3-dione and tetronic acid to yield stable 1,4-diionic imidazolium betaines in excellent yields.

Phosphine Organocatalysis

The hallmark of nucleophilic phosphine catalysis is the initial nucleophilic addition of a phosphine to an electrophilic starting material, producing a reactive zwitterionic intermediate, generally under mild conditions. In this Review, we classify nucleophilic phosphine catalysis reactions in terms of their electrophilic components. In the majority of cases, these electrophiles possess carbon-carbon multiple bonds: alkenes (section 2), allenes (section 3), alkynes (section 4), and Morita-Baylis-Hillman (MBH) alcohol derivatives (MBHADs; section 5). Within each of these sections, the reactions are compiled based on the nature of the second starting material-nucleophiles, dinucleophiles, electrophiles, and electrophile-nucleophiles. Nucleophilic phosphine catalysis reactions that occur via the initial addition to starting materials that do not possess carbon-carbon multiple bonds are collated in section 6. Although not catalytic in the phosphine, the formation of ylides through the nucleophilic addition of phosphines to carbon-carbon multiple bond-containing compounds is intimately related to the catalysis and is discussed in section 7. Finally, section 8 compiles miscellaneous topics, including annulations of the Hüisgen zwitterion, phosphine-mediated reductions, iminophosphorane organocatalysis, and catalytic variants of classical phosphine oxide-generating reactions.

2-Picoline catalyst-triggered [2 + 2 + 2] cycloaddition-type reaction of acetylenedicarboxylates, aldehydes and alkenes

2-Picoline efficiently catalyzes the formation of α,β-enones from acetylenedicarboxylates and aldehydes in the presence of alkenes, thereby leading to pyrans in moderate to good yields with complete regioselectivities. This synthetic method of pyrans is represented as a first example of catalytic and direct [2 + 2 + 2] cycloaddition of three different components under the metal-free conditions.

Diastereoselective synthesis of highly functionalized polycyclic benzosultams via tandem cyclisations of cyclic N-sulfonylimines with in situ generated Huisgen 1,4-dipoles

The tandem cycloadditions of cyclic N-sulfonylimines with in situ generated Huisgen 1,4-dipoles underwent readily, and delivered 1,2,3,4-tetrahydropyrimidine-fused benzosultams in acceptable chemical yields with excellent diastereoselectivities.

A new protocol for the consecutive alpha- and beta-activation of propiolates towards electrophiles, involving conjugate addition of tertiary amines and intramolecular silyl migration

Herein, we present a novel approach for the consecutive alpha- and beta-activation of conjugated alkynes and demonstrate the application of this methodology towards the C-C bond-forming reactions of propiolates. This new concept is based on the 1,4-addition of a tertiary amine to a conjugated alkyne, followed by an aldol-type addition to an aldehyde and subsequent intramolecular silyl migration. This sequential process is generally applicable for 3-trimethylsilylpropiolates. The combination of methyl 3-trimethylsilylpropiolate, 1,4-diazobicyclo[2.2.2]octane (DABCO), and aromatic aldehydes brought about domino-type C-C bond formations to afford highly functionalized olefins as the major products. On the other hand, aliphatic aldehydes, including the sterically demanding aromatic aldehyde, 2,6-dimethylbenzaldehyde, produced alkyne derivatives as the sole products from the reaction, presumably, by the reaction pathway common to the first cases. The intramolecular version of the reaction was successfully applied to the cyclization of trimethylsilylpropiolic esters derived from salicylaldehydes, leading to a new formylcoumarin synthesis. Studies of the reaction mechanisms are also described.

Further Characterization of Mitsunobu-Type Intermediates in the Reaction of Dialkyl Azodicarboxylates with P(III) Compounds

Structural characterization of compounds analogous to the proposed intermediates in the Mitsunobu esterification process is achieved by the combined use of NMR spectroscopy and X-ray diffractometric studies. The results show that compounds (t-BuNH)P(mu-N-t-Bu)(2)P[(N-t-Bu)(N-(CO(2)R)-N(H)(CO(2)R))] [R = Et (11), i-Pr (12)], obtained by treating [(t-Bu-NH)P-mu-N-t-Bu](2) (10) with diethylazodicarboxylate (DEAD) or diisopropylazodicarboxylate (DIAD), respectively, have a structure with the NH proton residing between the two nitrogen atoms ((P)N(t-Bu) and (P)N-N(CO(2)Et)); this is the tautomeric form of the expected betaine (t-BuNH)P(mu-N-t-Bu)(2)P(+)[(NH-t-Bu)(N-(CO(2)R)-N(-)(CO(2)R)]. Treatment of ClP(mu-N-t-Bu)(2)P[(N-t-Bu){N-(CO(2)-i-Pr)-N(H)(CO(2)-i-Pr)] (6) with 2,6-dicholorophenol affords (2,6-Cl(2)-C(6)H(3)-O)P(mu-N-t-Bu)(2)P(+)[(NH-t-Bu){N[(CO(2)i-Pr)(HNCO(2)i-Pr)]}](Cl(-))(2,6-Cl(2)-C(6)H(3)-OH) (14) that has a structure similar to that of (CF(3)CH(2)O)P(mu-N-t-Bu)(2)P(+)[(NH-t-Bu){N[(CO(2)i-Pr)(HNCO(2)i-Pr)]}](Cl(-)) (13), but with an additional hydrogen bonded phenol. Both of these have the protonated betaine structure analogous to that of Ph(3)P(+)N(CO(2)R)NH(CO(2)R)(R'CO(2))(-) (2) proposed in the Mitsunobu esterification. Two other compounds, (ArO)P(mu-N-t-Bu)(2)P(+)(NH-t-Bu){N(CO(2)i-Pr)(HNCO(2)i-Pr)}(Cl(-)) [Ar = 2,6-Me(2)C(6)H(3)O- (15) and 2-Me-6-t-Bu-C(6)H(3)-O- (16)], are also prepared by the same route. Although NMR tube reactions of 11 or 12 with tetrachlorocatechol, catechol, 2,2'-biphenol, and phenol revealed significant changes in the (31)P NMR spectra, attempted isolation of these products was not successful. On the basis of (31)P NMR spectra, the phosphonium salt structure (t-BuNH)P(mu-N-t-Bu)(2)P(+)[(HN-t-Bu){N-(CO(2)R)-N(H)(CO(2)R)](ArO(-)) is proposed for these. The weakly acidic propan-2-ol or water did not react with 11 or 12. Treatment of 12 with carboxylic acids/ p-toluenesulfonic acid gave the products (t-BuNH)P(mu-N-t-Bu)(2)P(+)[(HN-t-Bu){N-(CO(2)-i-Pr)-N(H)(CO(2)-i-Pr)](ArCO(2)(-)) [Ar = Ph (18), 4-Cl-C(6)H(4)CH(2) (19), 4-Br-C(6)H(4) (20), 4-NO(2)-C(6)H(4) (21)] and (t-BuNH)P(mu-N-t-Bu)(2)P(+)[(HN-t-Bu){N-(CO(2)-i-Pr)-N(H)(CO(2)-i-Pr)](4-CH(3)-C(6)H(4)SO(3)(-)) (22) that have essentially the same structure as 2. Compound 18 has additional stabilization by hydrogen bonding, as revealed by X-ray structure determination. Finally it is shown that the in situ generated (t-BuNH)P(mu-N-t-Bu)(2)P(+)[(HN-t-Bu){N-(CO(2)Et)-N(H)(CO(2)Et)](4-NO(2)-C(6)H(4)CO(2)(-)) can also effect Mitsunobu esterification. A comparison of the Ph(3)P-DIAD system with the analogous synthetically useful Ph(3)P-dimethyl acetylenedicarboxylate (DMAD) system is made.

Facile Synthesis of Highly Substituted 3-Aminofurans from Thiazolium Salts, Aldehydes, and Dimethyl Acetylenedicarboxylate

[reaction: see text] A facile preparation of 3-aminofuran derivatives via multicomponent reactions of thiazole carbenes, aldehydes, and dimethyl acetylenedicarboxylate (DMAD) is reported. In this process, the thiazole carbenes, generated in situ from thiazolium salts, reacted with aldehydes and DMAD at -78 to 0 degree C in CH(2)Cl(2) to afford the substituted furans in moderate to good yields. Eight substituted thiazolium salts were employed as carbene precursors in the reaction. Besides aryl aldehydes, alpha,beta-unsaturated aldehydes, aliphatic aldehydes, and arenedial were also investigated and found to be applicable to this reaction.

Unexpected Reaction of Dimethyl Acetylenedicarboxylate with in Situ Generated Arylketenes Catalyzed by 1-Methylimidazole

[reaction: see text]. An unexpected 1-methylimidazole-catalyzed reaction of dimethyl acetylenedicarboxylate (DMAD) with in situ generated arylketenes leading to the synthesis of dimethyl 2-arylidenesuccinates under mild conditions is described. A plausible mechanism has been proposed.