Cyclobutanone selective reduction

Modified Wolff-Kishner methods work well on ordinary cyclobutanones. Generally, the hydrazones are made at fairly mild reaction temperatures, base is added and the cyclobutane is distilled directly from the hot reaction mixture.237,272 279-284 The hydrazone can also be isolated prior to the reduction.285 The relatively facile reduction of cyclobutanones which occurs before that of larger ring ketones can be utilized in the selective reduction of cyclobutanones in the presence of, for example, a cyclohexanone, i.e. pentaspiro[3.1.3.3.3.3]heneicosane-5,11,19-trione was reduced in a stepwise manner to pentaspiro[3.1.3.3.3.3]heneicosane-5-one.237... 

Ruvn—>RuIV) the fact that it selectively oxidizes cyclobutanol to cyclobutanone and ferf-Bu(Ph)CHOH to the corresponding ketone, militates against free-radical intermediates and is consistent with a heterolytic, two-electron oxidation [103, 104]. Presumably, the key step involved /1-hydride elimination from a high-valent, for example, alkoxyruthenium(VII), intermediate followed by reoxidation of the lower-valent ruthenium by dioxygen. However, as shown in Fig. 18, if this involved the Ru(VII)/Ru( V) couple the reoxidation would require the close proximity of two ruthenium centres, which would seem unlikely in a polymer-supported catalyst. A plausible alternative, which can occur at an isolated ruthenium centre, involves the oxidation of a second molecule of alcohol, resulting in the reduction of ruthenium(V) to ruthenium(III), followed by reoxidation of the latter to ruthenium(VII) by dioxygen (Fig. 18). 

In hydrogenolyses with HAICU, the dimethyl acetals of cyclobutanone and cyclohexanone are cleaved more slowly than that of 3-pentanone, while those of cyclopentanone and cycloheptanone are cleaved more rapidly (Table 1), as would be expected for a carbonium ion process. The differences in rate are small, suggesting that carbonium ion character is not strongly developed in the transition state. With the dimethyl acetal of 4-t-butylcyclohexanone, the hydride addition step occurs with strongly predominating axial addition when HAlCh is used Zn(BH4)2 with TMS-Cl, and TMS-H with TMSO-Tf are less selective (Table 2). Equatorial attack predominates, however, in the reduction of the ketone itself with TBDMS-H and TBDMS-OTf. ... 

The synthesis of ( )-isodihydronepetalactone (114) is dependent upon the highly stereoselective hydrolysis of the cyclo-adduct (115) to (116) which on reductive cleavage of the cyclobutanone ring yields, after hydrolysis, (114) accompanied by minor amounts of the two lactones (117). Selective monohydroboration-... 

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