Novel methods to constrained phosphorus compounds and functional oligomers.

摘要

Transition metal-catalyzed strategies toward the development of conformationally constrained alpha-Boc-aminophosphonates and alpha-thiophosphonate derivatives are described. This particular approach exploited versatile tert-butylphosphonoacetate moieties to derive an array of mono- and bicyclic alpha-hetero-phosphonate systems. Amino groups were introduced via Curtius rearrangement, while the thio moiety was incorporated using a sulfur-ylide generation/rearrangement sequence. The molecular constraint in all systems was incorporated using either the ring-closing metathesis (RCM) reaction catalyzed by the first generation Grubbs catalyst or intramolecular cyclopropanation mediated by Rh2(OAc) 4.;The investigation of substituent effects in the double diastereotopic differentiation of alpha-diazophosphonates using intramolecular cyclopropanation catalyzed by Rh2(OAc)4 is also described. Carbene facial selectivity in these transformations was dictated by substrate control in either of two ways: (i) exploitation of (R)-pantolactone as an auxiliary incorporated into the carboester functionality while probing olefinic substituent effects, or (ii) utilization of chiral, nonracemic allylic alcohols incorporated into the phosphonate moiety. Excellent levels of olefin selectivity along with good diastereofacial selectivity were realized in both approaches.;The synthetic utility of ring-opening metathesis polymerization (ROMP)-derived oligomers as scavengers (both electrophilic and nucleophilic) and reagents, specifically benzylating agents, is also reported. Exploitation of (i) chemically-tagged scavengers, whereby the polymerization event takes place after the desired reaction, (ii) high-load, soluble oligomeric scavengers that can be precipitated from solution by solvent manipulation, and (iii) high-load, insoluble oligomeric scavengers is described. The spent oligomers were removed from the reaction mixture by simple filtration in all three cases. The benzylating agent described consisted of oligomeric sulfonate esters. Following amino-alkylation, these polymers could also be precipitated and removed via filtration, leaving the desired products in high yield and purity.