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The photochemical fragmentation of phosphine oxides with the 2-phosphabicyclo[2.2.2]octene framework constitutes a useful method for the generation of methylene(oxo)phosphoranes, R-P(O)=CH2. The previously uncharacterized and highly reactive P-phenyl and P -methyl derivatives were prepared and trapped with alcohols as phosphinates. The fragmentation also occurred when alkoxy substituents were present on phosphorus, but significant amounts of dialkyl phosphites were formed as by-products. Some new observations on the photochemical fragmentation of the 7-phosphanorbornene system have also been made. Contrary to literature reports, this system is resistant to fragmentation and does not extrude the 2-coordinate phosphoryl species. Fragmentation with loss of the phosphorus bridge does occur readily when an alcohol is also present in the medium. The data support a mechanism in which an initial photo-promoted addition reaction of the 7-phosphanorbornene and the alcohol occurs to form a 5-coordinate species, which undergoes the fragmentation. Thermal fragmentation of the 7-phosphanorbornenes is slow, but does appear to release the 2-coordinate phosphoryl species.We have demonstrated in several recent studies (1-4) that certain unsaturated bicyclic frameworks containing phosphorus functions can be fragmented in solution to release a simple phosphorus-containing moiety. The nature of the bond breaking process leaves phosphorus in these fragments in a condition of low coordination (number of attached atoms) for the particular oxidation state concerned, and the method has proved of practical value for the synthesis of several low coordination species. As a general rule, low-coordination phosphorus species are of very high reactivity and some types cannot be directly observed or isolated even when stabilization through kinetic or thermodynamic effects is attempted. In such cases, their intermediacy in chemical processes is usually demonstrated by trapping reactions. We continue to explore applications of the ring fragmentation approach in the low-coordination chemistry of phosphorus, and in this paper we will describe the first extension of our methods to the generation of two types of the 3-coordinate methylene(oxo)-

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In view of the interest of bicyclic systems containing heteroatoms for synthetic and stereochemical investigations, the incorporation of germanium into the bicyclic framework is achieved through ring closure of the bis‐Grignard reagent of the precursor system (I) and dichlorogermanes (II).

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