Dominic V Mcgrath
Publications
Abstract:
Efficient preparation of a series of four chiral, nonracemic AB2 monomers suitable for the construction of dendrimers is presented. Monomers 1-4 possess the common structural features of a diphenolic moiety and a benzylic or aliphatic hydroxyl which render these molecules suitable for convergent dendrimer synthesis. The same basic, high-yielding, five-step sequence is employed for 1-4. Stilbene derivatives 13 and 14 are prepared by a Horner-Wadsworth-Emmons modified Wittig reaction between 3,5- or 3,4-bis(benzyloxy)benzaldehyde (8 and 10) and an ester-substituted benzylphosphonate (11 or 12). Cinnamate derivatives 21 and 22 are prepared similarly from 8 and 10 and triethyl phosphonoacetate. Chirality is introduced in the form of a 1,2-diol unit by Sharpless asymmetric dihydroxylation (AD) (>97% ee in all cases). Protection of the 1,2-diols as their acetonide derivatives provides dioxolane intermediates 17, 18, 25, and 26. Reduction of the ester groups followed by hydrogenolysis of the benzyl ethers yields AB2 monomers 1-4 in 57-67% overall yield from 8 and 10.
Abstract:
(Formula presented) Benzyl aryl ether dendrimers containing photosensitive, veratryl-based o-nitrobenzyl AB linkages (bold bonds) were prepared to the third generation and shown to undergo site-specific degradation when irradiated with ultraviolet light.
The use of asymmetric phthalocyanines (Pcs) as platforms for the preparation of several asymmetric hexatriazolyl-monohydroxyphthalocyanines via copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction was investigated. Asymmetric Pcs 5a and 5b were prepared through statistical macrocyclization of phthalonitriles (Pns) 1a and 2 to give PMB-protected 4a and 4b, which afforded asymmetric Pcs 5a and 5b after acidic cleavage. The ‘ROMP-Capture-Release’ method as a synthetic approach to prepare asymmetric Pc 5b was also evaluated. TIPS-protection of the terminal alkynes was necessary to prevent cross-coupling during the ring-opening metathesis polymerization (ROMP) step. Zinc Pc 5b was successfully used as a scaffold for functional modification under CuAAC conditions using several azides bearing hydrophobic, photo-crosslinkable, or electroactive moieties. Monitoring the CuAAC reaction by both UV/Vis and FTIR spectroscopies provided insight into the role of azide equivalent, reaction time, and catalyst on reaction progress.
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