Oxocan-4-ones

RINGS WITH ONE OXYGEN ATOM 5.19.3.1 Oxocanes and Tetrahydrooxocins... 

The X-ray structure of the substituted oxocane laurencienyne, (429), shows that the ring has the BC-3 conformation (actually, the oxygen is at the mirror image 7 position of the boat-chair) and one chlorine atom is in an axial-like position. The other substituents are in unhindered positions on the ring (80TL2299,80CSC777). 

Eight-membered rings with one oxygen atom are named as oxocanes, oxocenes, or oxocines. The name A"-oxocene is frequently used for compounds with one double bond n = 2-4 indicates the position of the double bond. Oxocenes, however, are preferentially named as dihydo- or tetrahydrooxocines. The names of some selected oxocane and oxocine compounds are shown. 

A SmI2-promoted intramolecular Reformatsky-type reaction was used for the cyclization of 5-(bromoacetoxy)alde-hyde 96 (Scheme 17) <1998SL735>. This reaction provided a 2 1 epimeric mixture of the oxocan-2-ones 97 and 98 in 63% yield. The isomer 97 could be converted almost quantitatively into 98 (a precursor of (—)-octalactin A) by sequential Dess-Martin oxidation and NaBH4 reduction. 

Oxocyclooctane, or oxocane (XVII), has been studied by Anet and Degen. ) Although the 60 MHz proton spectrum of XVII shows little change at low temperatures, a single process is easily observed at 251 MHz. The a protons, for example, give one broad line at room temperature and two broad lines below —122 °C, with the rather small chemical shift difference of 0.18 ppm. No further change takes place at lower temperatures, and the 1 C nmr spectrum of XVII is temperature independent to —170 °C. 

The excision of the keto bridge present in tricyclo[5.3.1.1 ]dodecan-l 1-one taken from the work of Cha et al. on synthetic studies of taxol deserves special mention. Highly functionalized derivatives of bicyclo]5.3.1]undecane are obtained using the DIB/I2 system (Eq. 11) [38]. The fragmentation of a related derivative of oxabicyclo[3.3.1]nonan-9-one is used by the same authors as a key step in the synthesis of cK-2,8-disubstituted oxocanes (Eq. 12) [39]. 

The tub conformation for 9,1 l-diphenyl[5](2,6)-pyranophan-10-one has been determined by x-ray diffraction methods <90CB1587>. The structure of a novel dibenzo[c/]oxocane spiro compound, derived from the reaction of two benzocyclopropene and diphenylcyclopropenone, has also been reported <90ZN(B)1577>. 

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