Direct Catalytic Asymmetric and Regiodivergent N1- and C3- Allenylic Alkylation of Indoles

Herein we report a Pd-catalyzed asymmetric allenylic alkylation strategy for the direct functionalization of 1H-indoles by employing P-chiral BIBOP-type ligands. The regioselectivity (N1/C3) of this process can be switched efficiently. Using Cs2CO3 at elevated temperatures in MeCN, N1-alkylated indoles bearing axial chirality with a stereocenter non-adjacent (β) to the nitrogen are produced in good yields with high enantioselectivity and complete N1-regioselectivity regardless of the electronic properties and substitution patterns of diverse indoles. Using K2CO3 at room temperature in DCM, chiral C3-alkylated indoles can be obtained as well. Notably, we introduce a new class of tri-substituted allenylic electrophiles that proceeded through different pathways from di-substituted allenylic electrophiles.

Catalytic Asymmetric and Divergent Synthesis of Tricyclic and Tetracyclic Spirooxindoles: Controllable Site-Selective Electrophilic Halocyclization of 1,6-Enynes

Catalytic asymmetric and divergent assembly of tricyclic and tetracyclic 3,3'-pyrrolidonyl spirooxindoles was developed, involving a one-pot chiral Brønsted base catalyzed asymmetric propargylation for the synthesis of oxindole 1,6-enynes and a subsequent switchable site-selective and highly diastereoselective electrophilic iodocyclization of 1,6-enynes. In addition, antitumor properties of the newly synthesized compounds were evaluated.

Investigating light-use efficiency across a jack pine chronosequence during dry and wet years

Light-use efficiency (LUE) is the ability of vegetated canopies to use light for photosynthesis. Together with remote sensing estimates of canopy cover and meteorological inputs, LUE provides a physical basis for scaling carbon uptake processes from the stand to the global scale. A better understanding of the factors that control LUE will result in improved global estimates of carbon uptake from the terrestrial biosphere. To examine factors that control variability in LUE in stands of different ages during dry and wet conditions, we measured LUE in a chronosequence of four jack pine stands (recent clearcut (age 1-3), regenerating (age 8-9), immature (age 29-30) and mature (approximately 90 years old)) during one normal (2002), one very dry (2003) and two very wet (2004, 2005) growing seasons in Saskatchewan, Canada. Cumulative CO(2) fluxes decreased significantly at all sites during the drought year of 2003, as did mean LUE. Canopy foliage at the recently regenerating jack pine site increased by 19% between 2002 and 2003. Foliage growth rate was reduced by 6% between 2003 and 2004, and foliage biomass decreased by 6% from 2004 to 2005. Over the four years studied, LUE was greatest at the mature jack pine site and lower, but similar, at the other three sites. Mean growing-season LUE varied with mean soil water content at each site, except at that of the newly regenerating stand where soil water had little influence. Mean daily vapor pressure deficit typically had the greatest influence on variability in LUE at all sites. Diffuse versus direct radiation also had significant but varying effects on LUE in jack pine stands of different ages.

Effects of elevated carbon dioxide concentration and temperature on needle growth, respiration and carbohydrate status in field-grown Scots pines during the needle expansion period

We determined effects of long-term elevation of carbon dioxide concentration ([CO2]) and temperature on growth, respiration and carbohydrate concentration in needles of field-grown Scots pine (Pinus sylvestris L.) trees during the needle expansion period. Sixteen 20-year-old Scots pine trees were individually enclosed in closed-top, environmentally controlled chambers for 4 years in one of four environments: ambient conditions (CON); elevated [CO2] (EC); elevated temperature (ET); and a combination of both (EC + ET). Needle growth, carbohydrate concentration and dark respiration were measured at 3-day intervals throughout the needle expansion period. Dark respiration was partitioned into growth and maintenance components by regressing specific respiration rate against specific growth rate. In all treatments, growth, carbohydrate concentration and daily dark respiration rates of needles followed a similar seasonal pattern throughout the needle expansion period. Treatments EC, ET and EC + ET increased individual needle area and dry weight compared with the CON treatment. Carbohydrate concentrations in needles were increased by EC, but reduced by ET and EC + ET. Daily respiration rates increased slightly in the early stage of needle expansion and decreased gradually in the late stage when needles were exposed to EC, but increased consistently throughout the growing period when needles were exposed to ET or EC + ET. Partitioning of respiration into its two functional components showed that the growth respiration coefficient was unaffected by the treatments, whereas maintenance respiration was reduced by EC but increased by ET and EC + ET. Maintenance respiration was more sensitive to elevated temperature than growth respiration. We conclude that the difference in respiration rates between expanding and expanded needles should be taken into account when estimating the respiratory responses of needles to elevated [CO2] and temperature.