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

Cycloaddition reactions of allenylphosphonates (RO)(2)P(O)(R(1))C═C═CR(2)(2)] with dialkyl acetylenedicarboxylates, 1,3-diphenylisobenzofuran, and anthracene have been investigated and compared with those of allenoates (EtO(2)C)RC═C═CH(2)] and allenylphosphine oxides Ph(2)P(O)(R(1))C═C═CR(2)(2)] in selected cases. Allenylphosphonates (RO)(2)P(O)(Ar)C═C═CH(2) 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., (OCH(2)CMe(2)CH(2)O)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(2)CMe(2)CH(2)O)P(O)(H)C═C═CMe(2) possessing a terminal ═CMe(2) group with DMAD occurs by both 2 + 2] cycloaddition and ene reaction. While the reaction of ═CH(2) 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(2)C)RC═C═CH(2)] underwent exo-4 + 2] cyclization. Under similar conditions, allenylphosphonates with a terminal ═CR(2) group gave only β,γ]-cycloaddition products. An unusual ring-opening of a 4 + 2] cycloaddition product followed by ring-closing via 4 + 4] cycloaddition, as revealed by (31)P NMR spectroscopy, is reported. Anthracene reacted in a manner 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.