Stereoselective C,C-bond formation. Cyclizations of biradicals

The formation of C,C-bonds via photolytically generated biradicals can occur with high stereoselectivity. If triplet biradicals are involved, chiral induction is highly likely. Syntheses that occur only via singlet biradicals have a good chance to show a memory effect of chirality.

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Rhodium-Catalyzed Allylation Reactions

Synthesis ◽

10.1055/s-0037-1611784 ◽

2019 ◽

Vol 51 (13) ◽

pp. 2585-2631 ◽

Cited By ~ 12

Author(s):

Mahesh Bhagwan Thoke ◽

Qiang Kang

Keyword(s):

Natural Product ◽

Memory Effect ◽

Bond Formation ◽

Allylic Substitution ◽

Design And Development ◽

Diverse Range ◽

Current State ◽

Drug Synthesis ◽

Oxabicyclic Alkenes ◽

Made In

Rhodium-catalyzed allylation reactions are well known for their unique selectivity and reactivity due to the high memory effect of Rh as compared to other metals. These reactions involve the substitution of allylic rhodium intermediates with a diverse range of different nucleophiles, leading to C–C and C–heteroatom bond formation. Modern organic chemists are, however, interested in atom-economical protocols under greener pathways and following recent increased understanding of mechanistic aspects of Rh-catalyzed allylation via the hydrofunctionalization of allenes or alkynes, great strides have made in the design and development of new atom-economical protocols. In this article, we review this field from its beginning to current state.1 Introduction2 Rhodium-Catalyzed Allylic Substitution3 Rhodium-Catalyzed Allylation with Allenes4 Rhodium-Catalyzed Allylation with Alkynes5 Rhodium-Catalyzed Allylation with Dienes6 Rhodium-Catalyzed Allylation by ARO of Oxabicyclic Alkenes7 Rhodium-Catalyzed Enantioselective Allylation in Natural Product and Drug Synthesis8 Conclusion

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Catalytic asymmetric Nakamura reaction by gold(I)/chiral N,Nʹ-dioxide-indium(III) or nickel(II) synergistic catalysis

Nature Communications ◽

10.1038/s41467-021-23105-z ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Xinyue Hu ◽

Xiaoxue Tang ◽

Xiying Zhang ◽

Lili Lin ◽

Xiaoming Feng

Keyword(s):

Lewis Acid ◽

Bond Formation ◽

Experimental Investigations ◽

Powerful Method ◽

Dicarbonyl Compound ◽

Chiral Induction ◽

Synergistic Catalysis ◽

Synergistic Activation ◽

Carbon Carbon Bond ◽

Catalytic Asymmetric

AbstractIntermolecular addition of enols and enolates to unactivated alkynes was proved to be a simple and powerful method for carbon-carbon bond formation. Up to date, a catalytic asymmetric version of alkyne with 1,3-dicarbonyl compound has not been realized. Herein, we achieve the catalytic asymmetric intermolecular addition of 1,3-dicarbonyl compounds to unactivated 1-alkynes attributing to the synergistic activation of chiral N,N′-dioxide-indium(III) or nickel(II) Lewis acid and achiral gold(I) π-acid. A range of β-ketoamides, β-ketoesters and 1,3-diketones transform to the corresponding products with a tetra-substituted chiral center in good yields with good e.r. values. Besides, a possible catalytic cycle and a transition state model are proposed to illustrate the reaction process and the origin of chiral induction based on the experimental investigations.

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Use of 2½ D imaging in analysis of NiTi martensite

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100110192 ◽

1978 ◽

Vol 36 (1) ◽

pp. 610-611

Author(s):

G. M. Michal

Keyword(s):

Memory Effect ◽

Monoclinic Phase ◽

Reaction Path ◽

Structural Characteristics ◽

Salient Feature ◽

Martensite Phase ◽

Orientation Relationships ◽

Low Symmetry ◽

Hydride Phases ◽

Unusual Shape

Several TEM investigations have attempted to correlate the structural characteristics to the unusual shape memory effect in NiTi, the consensus being the essence of the memory effect is ostensible manifest in the structure of NiTi transforming martensitic- ally from a B2 ordered lattice to a low temperature monoclinic phase. Commensurate with the low symmetry of the martensite phase, many variants may form from the B2 lattice explaining the very complex transformed microstructure. The microstructure may also be complicated by the enhanced formation of oxide or hydride phases and precipitation of intermetallic compounds by electron beam exposure. Variants are typically found in selfaccommodation groups with members of a group internally twinned and the twins themselves are often observed to be internally twinned. Often the most salient feature of a group of variants is their close clustering around a given orientation. Analysis of such orientation relationships may be a key to determining the nature of the reaction path that gives the transformation its apparently perfect reversibility.

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Tensile Failure of 55-Nitinol Wire

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100113858 ◽

1975 ◽

Vol 33 ◽

pp. 46-47

Author(s):

F. I. Grace

Keyword(s):

Shape Memory ◽

Shape Memory Effect ◽

Memory Effect ◽

Stoichiometric Composition ◽

Tensile Failure ◽

Initial State ◽

Initial Shape ◽

Nitinol Wire ◽

Cscl Type ◽

Shear Transformation

An interest in NiTi alloys with near stoichiometric composition (55 NiTi) has intensified since they were found to exhibit a unique mechanical shape memory effect at the Naval Ordnance Laboratory some twelve years ago (thus refered to as NITINOL alloys). Since then, the microstructural mechanisms associated with the shape memory effect have been investigated and several interesting engineering applications have appeared.The shape memory effect implies that the alloy deformed from an initial shape will spontaneously return to that initial state upon heating. This behavior is reported to be related to a diffusionless shear transformation which takes place between similar but slightly different CsCl type structures.

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