Coarctate reactions

Transient carbene (9) is expected to be a reaction intermediate in the transformation of butadiyne-linked triazene (8) to alkyne-linked bis-2//-indazolcs (10).18 Experimental data and DFT calculations support carbene (9) as an intermediate in this stepwise, non-synchronous coarctate reaction. Methoxy(methylthio)carbene (12) has been observed by UV photoelectron spectroscopy after gas-phase decomposition of oxadiazoline (11).19 The oxadiazoline (13) allows the generation of the acetoxy(methoxy)carbene (14) 20 -pjjg reaC jvj y 0f (he latter with isocyanates has been explored. Such reactions generally yield methyl (acetylamino)oxoacetates (15). DFT calculations permitted interpretation of the experimental data. 

This an example of coarctate reaction in which two bonds are simultaneously formed and broken at an atom not following a cyclic pathway.94 The 13C KIEs for fragmentation of 50 at 150°C in diphenyl ether were determined for substrate at 65-84% conversion (Figure 19). 

Another example of coarctate reaction studied by means of 13C KIEs is the deoxygenation of styrene oxide 51 with dichlorocarbene.95... 

Birney, D. M. Electrocyclic ring openings of 2-fuiylcarbene and related carbenes a comparison between pseudopericycUc and coarctate reactions, J. Am. Chem. Soc. 2000,122,10917-10925. 

These interesting reactions represent a truly different basic form, which he labels coarctate reactions, generalized as two... 

It is therefore reasonable to postulate that the confinement of carbene 46, perhaps within the nanoscopic pores of CyDs and FAUs, would inhibit the fragmentation reaction and foster the 1,3-CH insertion. This reasoning is twofold (1) there may not be enough space within the hosts cavities for the unraveling process, 46—>47, and (2) distortion of the carbene s topology might concomitantly disfavor the coarctate TS and allow the 1,3-CH insertion, 46->48, to finally occur. 

Coarctate cyclization reactions using a conjugated ene—ene—yne precursor to form a heterocycle 12CC9441. 

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