Hunsdiecker reaction, modified, for

Hunsdiecker reaction, modified for preparation of 1-bromo-3-chlorocyclobutan9, 51, 106 Hydrazine, anhydrous, 50, 3, 4, 6... 

Methyl oxetane-2-carboxylate derivatives (e.g., 284), obtained by ring contraction of aldonolactones, have been employed for the synthesis (279) of the nucleoside / -noroxetanocin [9-(/ -D-eryt/iro-oxetanosyl)adenine, 304] and its a-anomer via an a-chloride obtained by a modified Hunsdiecker reaction. Displacement of chloride by adenine and debenzylation gave 304. The threo isomer of304, /J-epinoroxetanocin (305), was likewise synthesized from D-lyxono-1,4-lactone. The oxetane nucleosides display potent antiviral activity against the human immunodeficiency virus (HIV). 

This is a modified Hunsdiecker reaction which avoids some of the difficulties associated with the use of heavy metals, i.e. troublesome work up procedures and the need to use an excess of toxic oxidant. For this transformation there is no need to convert the acid into its PhI(02CR)2 derivative, since it is formed in situ using DIB. 

The best yields (51-89%) were for substrates with R1 =H and phenyl rings (R2 and/or R3), especially when containing an electron-donating group. This modified Hunsdiecker reaction was equally successful with DIB conventional methods for this transformation of a,/J-unsaturated acids gave poor results. DIB has also been used for the photochemical halodecarboxylation of acids (Section 4.8.1). 

Hmtsdiecker Cristol reaction. (I, 657). A detailed procedure for the preparation of l-bromo-3-chlorocyclobutanc by the modified Hunsdiecker reaction has been published. A l-l. three-necked, round-bottomed flask wrapped with aluminum foil to exclude light and equipped with a mechanical stirrer, a reflux condenser, and an addition funnel, is charged with 37 g. (0.17 mole) of red mercuric oxide and 330 ml. 

The classical Hunsdiecker reaction was utilized in the laboratory of P.J. Chenier for the preparation of a highly strained cyclopropene, tricyclo[3.2.2.0 " ]non-2(4)-ene. The Diels-Alder cycloaddition was used to prepare the bicyclic 1,2-diacid, which surprisingly failed to undergo the Cristol-Firth modified Hunsdiecker reaction, most likely due to the unreactive nature of the diacid mercuric salt. However, the classical conditions proved to work better to afford the bicyclic 1,2-dibromide in modest yield. Treatment of this dibromide with f-BuLi generated the desired strained cyclopropene, which was trapped with diphenylisobenzofuran (DPIBF). 

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