Helical poly(isocyanides)

Nolte, Roeland J. M.

doi:10.1039/cs9942300011

Cited by 245 publications

(140 citation statements)

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“…On the basis of the X-ray analysis of LC samples, L-20 was found to possess a rigid-rod 15/4 helix; this helical structure is similar in structure to that postulated for a long time for helical polyisocyanides (4/1 helix). 5,51,86,87 Polymerization of the same L-Ala-bound isocyanide monomer with the m-ethynediyl Pt-Pd catalyst promoted the living polymerization, 73 which, interestingly, simultaneously produced almost completely right-(L-20c) and left-handed (L-20d) helices with different molecular weights and narrow molecular weight distributions (Figure 10b). …”

Section: Synthesis and Structures Of Helical Polymers E Yashimamentioning

confidence: 99%

“…85 Given the success in visualizing the helical structures of dynamic helical poly(phenylacetylene)s by AFM, the same procedure has been applied to the L-Ala-bound helical polyisocyanide (L-20). The helical structures of polyisocyanides have been postulated to be a 4/1 helix (2), 5,51,86,87 but the exact helical structures and their absolute helical senses remain unknown except for h-27-Me. 69 We previously found that diastereomeric right-and left-handed helical polyisocyanides (L-20) were formed by an unprecedented helix-sense-controlled polymerization of an enantiomerically pure phenyl isocyanide bearing the same L-Ala residue with a long n-decyl chain as the pendant using an achiral nickel catalyst (NiCl 2 ) in different solvents, such as CCl 4 and toluene, at different temperatures (Figure 10a).…”

Section: Synthesis and Structures Of Helical Polymers E Yashimamentioning

confidence: 99%

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Synthesis and structure determination of helical polymers

Yashima

2010

Polym J

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During the last decade, remarkable progress in developing synthetic helical polymers with a controlled helical sense has been achieved. However, the exact helical structures of most of the already prepared synthetic helical polymers remain unsolved. In this review, the recent progress in the synthesis of helical polymers and their structural determination, including helical pitch and handedness based on X-ray diffraction and spectroscopic measurements, together with high-resolution atomic force microscopy, is described. Polymer Journal (2010) 42, 3-16; doi:10.1038/pj.2009 Keywords: atomic force microscopy; circular dichroism; helical polymer; helical structure; X-ray diffractionThe helix is a unique structure as observed in nature from microscopic to macroscopic levels and is inherently chiral. Inspired by biological helices, such as DNA and proteins, chemists have been challenged to synthesize helical polymers with a controlled helical sense that aims not only to mimic biological helical structures but also to develop chiral materials for the separation of enantiomers and asymmetric catalysis. [1][2][3][4][5][6][7][8][9][10][11][12] The history of synthetic helical polymers with optical activity extends back to the 1960s when Pino and Lorenzi 13 investigated the structural and chiroptical properties of isotactic vinyl polymers prepared by the polymerization of a-olefins bearing optically active substituents. Although helical polyolefins are totally dynamic in nature and consist of short helical segments separated by frequently occurring helical reversals among disordered, random coil conformations, 14 this study was significant in the field of synthetic helical polymers, from which a number of helical polymers have been synthesized.On the basis of the pioneering studies by Nolte et al., 15 Okamoto et al. 16 and Green et al., 17 the existing synthetic helical polymers that exhibit an optical activity solely because of their macromolecular helicity can be classified into two categories with respect to their helix inversion barriers, that is, static and dynamic helical polymers (Figure 1). 9,12 Optically active helical polymers, such as poly(triphenylmethyl methacrylate) (1), 16 poly(t-butyl isocyanide) (2) 15 and polychloral (3), 18 have a sufficiently high helix inversion barrier and belong to the family of static helical polymers. Therefore, these helical polymers with either a right-or left-handed helix can be prepared by the helix-sense-selective polymerization of the corresponding achiral monomers using chiral catalysts or initiators under kinetic control. On the other hand, dynamic helical polymers, such as polyisocyanates (8) 17 and polysilanes (9), 19 possess a very low helix inversion barrier.As a consequence, they consist of interconvertible right-and lefthanded helical segments separated by rarely occurring helical reversals, as demonstrated by Green et al.,6,20,21 so that a preferred-handed helical conformation can be induced in the presence of a small amount of chiral residues at the pendant 6 or ter...

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Section: Synthesis and Structures Of Helical Polymers E Yashimamentioning

confidence: 99%

Section: Synthesis and Structures Of Helical Polymers E Yashimamentioning

confidence: 99%

Synthesis and structure determination of helical polymers

Yashima

2010

Polym J

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“…Details of these helical polymers have been thoroughly reviewed elsewhere. [1][2][3][4][5] Besides these helical polymers, we recently succeeded in inducing a conceptually new helicity on optically inactive polyacetylenes upon complexation with optically active small molecules capable of interacting with the polymers. This article describes our recent studies on helicity induction of polyacetylenes through noncovalent, chiral acid-base interactions together with chiral recognition ability of optically active polyacetylenes as a chiral stationary phase (CSP) for HPLC.…”

Section: Introductionmentioning

confidence: 99%

Chiral and Chirality Discrimination on Helical Polyacetylenes

Yashima

2002

ANAL. SCI.

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“…Insightful proposals have been made in this regard, where control of conformation is dictated by the avoidance of nonbonded interactions between methyl groups in energetically preferred acyclic conformations (18,19). Within a three-dimensional array, alternating C-methyl groups in an acyclic chain are better accommodated in synoriented motifs as compared with anti-oriented motifs, reminiscent of helical isotactic hydrocarbon polymers such as polypropylene (20)(21)(22)(23)(24).…”

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confidence: 99%

Total synthesis of the cytotoxic cyclodepsipeptide (-)-doliculide: The “ester” effect in acyclic 1,3-induction of deoxypropionates

Hanessian

Mascitti

Giroux

2004

Proc. Natl. Acad. Sci. U.S.A.

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The total synthesis of the marine cyclodepsipeptide (؊)-doliculide is described. An acyclic (2S,4S,6R)-trimethyl alkanoic acid precursor to the ''hydrocarbon'' portion of doliculide was synthesized starting with L-ascorbic acid based on a stereocontrolled iterative conjugate addition of lithium dimethylcuprate to acyclic ␦-Cmethyl ␣,␤-unsaturated ester derivatives. syn͞syn selectivity was achieved by relying on 1,3-induction in preferred folded conformations that avoid 1,5-syn-pentane interactions in the transition states. The nature of the ester moiety seems to play an important role in determining the syn͞anti ratios of C-methyl adducts. The 1-methyl-1-cyclopentyl ester group was found to confer the best syn selectivity to the cuprate addition products, especially in seven-carbon enoates.

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Helical poly(isocyanides)

Cited by 245 publications

References 34 publications

Synthesis and structure determination of helical polymers

Synthesis and structure determination of helical polymers

Chiral and Chirality Discrimination on Helical Polyacetylenes

Total synthesis of the cytotoxic cyclodepsipeptide (-)-doliculide: The “ester” effect in acyclic 1,3-induction of deoxypropionates

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