An investigation of the effect of organic soil constituents on boron adsorption

• Main Author: Gu, Baohua
• Language: English
• Published: University of British Columbia 2010
• Online Access: http://hdl.handle.net/2429/25886

The preparation and synthetic utility of a number of structurally interesting donor-acceptor reagents is described. It has been found that protonative deconjugations of geometrically isomeric β-trimethyl-stannyl-α,β-unsaturated esters are highly stereospecific. Thus, treatment of the esters (131) and (137) with lithium diisopropylamide in THF or THF-HMPA followed, in each case, by transfer of the resultant solution to a cold (-98°C) solution of acetic acid in ether, provided exclusively the alkyl 3-trimethylstannyl-3-alkenoates (167) and (173), respectively. Ethyl (Z) and (E)-3-trimethylstannyl-3-pentenoates were converted into the chlorides (99) and (100), respectively. Transmetalation of (99) afforded (204), which was transformed into the Grignard reagent (218) . Both (204) and (218) serve effectively as conjunctive reagents which are synthetically equivalent to the (E)-d³,a⁵-2-pentene synthon (200). For example, copper(I)-catalyzed conjugate addition of (218) to enones and subsequent intramolecular alkylation of the resultant products form the basis of a new (Z)-ethylidenecyclopentane annulation process [(220) → (222)]. Interestingly, although transmetalation of (100) also occurred smoothly, the resultant lithio reagent (207) self-annihilated rapidly even at low temperatures to give ethylidene-cyclopropane. The annulation method described above played a key role in short syntheses of (±)-oplopanone (257), (±)-8-epi-oplopanone (323), and (±)-anhydro-oplopanone (258). Thus (Z)-ethylidenecyclopentane annulation of 4-isopropyl-2-cyclohexen-l-one provided the bicyclic ketone (307). Suitable functional group manipulations transformed (307) into (±)-(257), (±)-(323), and (±)-(258). Reaction of 1-alkyn-3-ols with Me₃SnCu.Me₂S-MeOH, [Me₃SnZn(t-Bu)₂]Li-CuCN, or [Me3SnZnEt2]Li-CuCN provided, in varying ratios, the vinylstannanes (109) and (339). Orthoester Claisen rearrangement of (109) and (339) afforded the esters (357) and (363), respectively. Ethyl (Z)-4-trimethylstannyl-4-hexenoate was transformed into the chloride (370). Compound (370) is a convenient precursor of reagents (371) and (374) which are synthetically equivalent to the (E)-d³,a⁶-2-hexene synthon (379). For instance, the Grignard reagent (374) served as a pivotal species in the development of a new six-membered annulation method [(101) → (380)]. [See Thesis for Diagrams] === Land and Food Systems, Faculty of === Graduate