1,3-Halogen shifts occuring via four-membered ring halonium ion intermediates in the solvolyses of 3-halo-1-butyl trifluoromethanesulfonates

An new overall lower energy pathway for the amine-catalysed Morita-Baylis-Hillman reaction is proposed from computations at the M06-2X/6-311++G(d,p) level. The pathway involves proton-transfer from the ammonium ion to the alkoxide formed from the aldol reaction through a seven-membered ring transition state (TS) structure followed by highly exothermic Hofmann elimination through a five-membered ring TS structure to form the product and also release the catalyst to carry on with the process all over again.

Download Full-text

An Alternate Energy-Conserved Pathway for the Morita-Baylis-Hillman (MBH) Reaction

10.26434/chemrxiv.12011673 ◽

2020 ◽

Author(s):

Veejendra Yadav

Keyword(s):

Proton Transfer ◽

Transition State ◽

Lower Energy ◽

Aldol Reaction ◽

Membered Ring ◽

Ammonium Ion ◽

Alternate Energy ◽

Ring Transition State ◽

Mbh Reaction

An new overall lower energy pathway for the amine-catalysed Morita-Baylis-Hillman reaction is proposed from computations at the M06-2X/6-311++G(d,p) level. The pathway involves proton-transfer from the ammonium ion to the alkoxide formed from the aldol reaction through a seven-membered ring transition state (TS) structure followed by highly exothermic Hofmann elimination through a five-membered ring TS structure to form the product and also release the catalyst to carry on with the process all over again.

Download Full-text

Catalytic Synthesis of Cyclic Guanidines via Hydrogen Atom Transfer and Radical-Polar Crossover

10.26434/chemrxiv.13318421.v1 ◽

2020 ◽

Author(s):

Shunya Ohuchi ◽

Hiroki Koyama ◽

Hiroki Shigehisa

Keyword(s):

Hydrogen Atom ◽

Functional Group ◽

Hydrogen Atom Transfer ◽

Catalytic Synthesis ◽

Membered Ring ◽

Biologically Active ◽

Atom Transfer ◽

Powerful Method ◽

Protective Groups ◽

The Common

A catalytic synthesis of cyclic guanidines, which are found in many biologically active compounds and natu-ral products, was developed, wherein transition-metal hydrogen atom transfer and radical-polar crossover were employed. This mild and functional-group tolerant process enabled the cyclization of alkenyl guanidines bearing common protective groups, such as Cbz and Boc. This powerful method not only provided the common 5- and 6-membered rings but also an unusual 7-membered ring. The derivatization of the products afforded various heterocycles. We also investigated the se-lective cyclization of mono-protected or hetero-protected (TFA and Boc) alkenyl guanidines and their further derivatiza-tions.

Download Full-text

Convergent Total Synthesis of Principinol D, a Rearranged Kaurane Diterpenoid

10.26434/chemrxiv.7865168.v4 ◽

2019 ◽

Author(s):

Timothy Newhouse ◽

Aneta Turlik ◽

Yifeng Chen ◽

Anthony Scruse

Keyword(s):

Total Synthesis ◽

Natural Product ◽

Late Stage ◽

Membered Ring ◽

Entry Point ◽

Ketone Reduction ◽

Coupling Approach

<div> The total synthesis of principinol D, a rearranged kaurane diterpenoid, is reported. This grayanane natural product is constructed via a convergent fragment coupling approach, wherein the central 7-membered ring is synthesized at a late stage. The bicyclo[3.2.1]octane fragment is accessed by a Ni-catalyzed α-vinylation reaction. Strategic reductions include a diastereoselective SmI2-mediated ketone reduction with PhSH and a new protocol for selective ester reduction in the presence of ketones. The convergent strategy reported herein may be an entry point to the larger class of kaurane diterpenoids. </div>

Download Full-text

Isomerization of the Isoprene Hydroxy Nitrates and Formation of Orthonitrite Compounds

10.26434/chemrxiv.8317127 ◽

2019 ◽

Author(s):

Gabriel da Silva

Keyword(s):

Hydroxy Group ◽

Peroxyl Radical ◽

Branching Fractions ◽

Membered Ring ◽

Low Energy ◽

Peroxyl Radicals ◽

Aerosol Formation ◽

Subsequent Removal ◽

Ring Compounds ◽

Group Migration

Atmospheric oxidation of isoprene produces significant yields of eight unique nitrate 11 compounds, each with a β- or δ-hydroxy group. These isoprene hydroxy nitrates (ISOPNs) 12 significantly impact upon global NOx budgets, O3 levels, and aerosol formation. 13 Uncertainties exist, however, in our understanding of ISOPN chemistry, particularly in their 14 yields from the reaction of isoprene peroxyl radicals with NO. This study describes novel 15 isomerization reactions of the ISOPNs, identified through the application of computational 16 chemistry techniques. These reactions produce saturated polycyclic orthonitrite compounds 17 via attack of the R–NO2 group on the vinyl moiety. For the δ-hydroxy nitrates, low-energy 18 isomerization pathways exist to six-membered ring compounds that are around 5 kcal mol-1 19 exothermic. These reactions proceed with barriers around 15 kcal mol-1 below the 20 respective peroxyl radical + NO reactants and yield orthonitrites that can further isomerize 21 to β-hydroxy ISOPNs. Moreover, the δ-hydroxy nitrates can directly interconvert with their β 22 substituted counterparts via NO3 group migration, with barriers that are lower yet. It follows 23 that β-hydroxy nitrates may be stabilized in the δ-hydroxy form, and vice versa. Moreover, 24 the lowest-energy pathway for dissociation of the δ-hydroxy ISOPNs is for the formation of 25 β-hydroxy alkoxyl radicals, and because of this established branching fractions between the 26 various isoprene peroxyl radicals may require re-evaluation. The results presented here also 27 suggest that ISOPNs may be stabilized to some extent in their saturated orthonitrite forms, 28 which has implications for both the total nitrate yield and for their subsequent removal by 29 OH, O3, and photolysis.

Download Full-text