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Intramolecular [2 + 2] cycloaddition reactions of alkynyl ether derived ketenes. A convenient synthesis of donor-acceptor cyclobutanes.

ABSTRACT: Mild thermolysis of tert-butyl alkynyl ethers furnishes aldoketenes, which undergo facile [2 + 2] cycloaddition reactions with pendant di- and trisubstituted alkenes. A wide variety of cis-fused cyclobutanones are produced in moderate to high diastereoselectivity and good to excellent yields by this method, and free hydroxyl groups are tolerated in the ene-ynol ether starting materials. Enol-ynol ethers also undergo efficient reaction to produce donor-acceptor cyclobutanes in high yields.

SUBMITTER: Tran V

PROVIDER: S-EPMC3244214 | biostudies-literature | 2011 Dec

REPOSITORIES: biostudies-literature

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Intramolecular [2 + 2] cycloaddition reactions of alkynyl ether derived ketenes. A convenient synthesis of donor-acceptor cyclobutanes.

Tran Vincent V Minehan Thomas G TG

Organic letters 20111121 24

Mild thermolysis of tert-butyl alkynyl ethers furnishes aldoketenes, which undergo facile [2 + 2] cycloaddition reactions with pendant di- and trisubstituted alkenes. A wide variety of cis-fused cyclobutanones are produced in moderate to high diastereoselectivity and good to excellent yields by this method, and free hydroxyl groups are tolerated in the ene-ynol ether starting materials. Enol-ynol ethers also undergo efficient reaction to produce donor-acceptor cyclobutanes in high yields. ...[more]

PMID: 22103709

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Project description:Donor-acceptor systems forming exciplexes are versatile models for the study of magnetic field effects (MFEs) on charge recombination reactions. The MFEs originate from singlet-triplet interconversion within transient radical ion pairs (RIPs), which exist in a dynamic equilibrium with the exciplexes. Here, we describe the synthesis and MFEs of the chain-linked N,N-dimethylaniline (DMA)/9-methylanthracene (MAnt) donor-acceptor system MAnt-(CH2) n -O-CH2-CH2-DMA for n = 6, 8, 10, and 16. The MFEs are found to increase with increasing chain length. Effects as large as 37.5% have been observed for the long-chain compound with n = 16. The solvent dependence of the MFEs at magnetic field intensity 75 mT is reported. For the range of solvent static dielectric constants ?s = 6.0-36.0, the MFEs go through a maximum for intermediate polarities, for which the direct formation of RIPs prevails and their dissociation and reencounter are balanced. Field-resolved measurements (MARY spectra) are reported for solutions in butyronitrile. The MARY spectra reveal that for n = 8, 10, 16, the average exchange interaction is negligible during the coherent lifetime of the radical pair. However, singlet-triplet dephasing broadens the lineshape; the shorter the linker, the more pronounced this effect is. For n = 6, a dip in the fluorescence intensity reveals a nonzero average exchange coupling of the order of ±5 mT. We discuss the field-dependence in the framework of the semiclassical theory taking spin-selective recombination, singlet-triplet dephasing, and exchange coupling into account. Singlet recombination rates of the order of 0.1 ns-1 and various degrees of singlet-triplet dephasing govern the spin dynamics. In addition, because of a small free energy gap between the exciplex and the locally excited fluorophore quencher pair, a fully reversible interconversion between the RIP, exciplex, and locally excited fluorophore is revealed by spectrally resolved MFE measurements for the long-chain systems (n = 10, 16).

Dataset Information

Intramolecular [2 + 2] cycloaddition reactions of alkynyl ether derived ketenes. A convenient synthesis of donor-acceptor cyclobutanes.

Publications

Intramolecular [2 + 2] cycloaddition reactions of alkynyl ether derived ketenes. A convenient synthesis of donor-acceptor cyclobutanes.

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