Phosphorverbindungen ungewöhnlicher Koordination, 5 [3+2]- sowie [4+2]-Cycloadditionsreaktionen an ein kinetisch stabilisiertes Phosphaalken/ Phosphorus Compounds with Unusual Coordination, 5 [3+2]- as well as [4+2]-Cycloaddition Reactions to a Kinetically Stabilized Phosphaalkene

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Abstract
Aliphatic diazo compounds display different reactivity towards the phosphaalkene 9: diazomethane, diazoethane and terf-butyl diazoacetate (10a-c) formally react with Si/P-insertion to give the hitherto unknown phosphaalkenes 12a-c. In contrast, 1-diazo-2.2-dim ethylpropane (10d) and diazotrimethylsilylmethane (10e) lead to the 1.2.4-diazaphospholes 15 and 17, respectively, if the primary products (11d , 14) are treated with sodium hydroxide in tetrahydrofuran. T he reaction of the nitrile oxides 18a-c with 9 yields the 1.2.4-oxazaphospholes 20a-c; the [3+2] cycloadducts 19a-c are assumed to occur as intermediates, which eliminate hexamethylsiloxane either spontaneously (19a, b) or with OH- -catalysis. Azide dipoles (21a-c) add to 9 with formation of 4.5-dihydro-1.2.3.4-phospholes (22a-c) which - instead of aromatization by hexamethyldisiloxane elimination - prefer fragmentation to 23 (→25 ) and imidoesters 24a-c; hydrolysis produces the pivaloyl amides 26a-c. The 1:2 reaction between 9 and the o-quinones 31a-d proceeds via [4+2] cycloadducts (32a-d) to produce the phosphoranes 34a-d by a subsequent [4+1] cycloaddition process.

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