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Cycloaddition Reactions of Allenylphosphonates and Related Allenes with Dialkyl Acetylenedicarboxylates, 1,3-Diphenylisobenzofuran, and Anthracene

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posted on 2011-02-04, 00:00 authored by K. V. Sajna, Ramesh Kotikalapudi, Manab Chakravarty, N. N. Bhuvan Kumar, K. C. Kumara Swamy
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)(R1)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 (OCH2CMe2CH2O)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 [(EtO2C)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 ring-closing via [4 + 4] cycloaddition, as revealed by 31P 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.

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