Cycloaddition reactions of allenylphosphonates and related allenes with dialkyl acetylenedicarboxylates, 1,3-Diphenylisobenzofuran, and anthracene

Abstract

Cycloaddition reactions of allenylphosphonates [(RO)2P(O) [(R1)C=C=CR22] with dialkyl acetylenedicarboxylates, 1,3-diphenylisobenzofuran, and anthracene have been investigated and compared with those of allenoates [(EtO2C)RC=C= CH2] and allenylphosphine oxides [Ph2P(O)(R 1)C=C=CR22] in selected cases. Allenylphosphonates (RO)2P(O)(Ar)C=C=CH2 with an α-aryl group preferentially undergo [4 + 2] cycloaddition with DMAD/DEAD under thermal activation, but in addition to the expected 1:1 (allene: DMAD) product, the reaction also leads to 1:2 as well as 2:1 products that were not reported before. When an extra vinyl group is present at the γ-carbon of allenylphosphonate [e.g., (OCH2CMe2CH2O)P(O) (Ph)C=C=CH(C=CHMe)], [4 + 2] cycloaddition takes place utilizing either the vinylic or the aryl end, but additionally a novel cyclization wherein complete opening of the [β,γ] carbon-carbon double bond of the allene is realized. In contrast to these, the reaction of allenylphosphonate (OCH 2CMe2CH2O)P(O)(H)C=C=CMe2 possessing a terminal =CMe2 group with DMAD occurs by both [2 + 2] cycloaddition and ene reaction. While the reaction of =CH2 terminal allenylphosphonates as well as allenylphosphine oxides with 1,3- diphenylisobenzofuran afforded preferentially endo-[4 + 2] cycloaddition products via [α,β] attack, the analogous allenoates [(EtO 2C)RC=C=CH2] underwent exo-[4 + 2] cyclization. Under similar conditions, allenylphosphonates with a terminal =CR2 group gave only [β,γ]-cycloaddition products. An unusual ring-opening of a [4 + 2] cycloaddition product followed by ringclosing via [4 + 4] cycloaddition, as revealed by 31PNMRspectroscopy, is reported. Anthracene reacted in amanner similar to 1,3-diphenylisobenzofuran, albeit with lower reactivity. Key products, including a set of exo- and endo- [4 + 2] cycloaddition products, have been characterized by single crystal X-ray crystallography. © 2011 American Chemical Society.