Spiro tetrahydrofurans from

These reductions can be combined with other transformations as exemplified by cyclopropane 120, which has been converted to the nitrile 122, the spiro lactone 123, and the functionalized spiro tetrahydrofuran 121 61). All products are eventually derived from cyclohexane carbaldehyde. 

Scheme 58 Synthesis of spiro-fused tetrahydrofurans from Prins-pinacol cascades by Cho et al. [66]...

Strong base treatment of the spiro salt 49 gives a benzyne (107) from which the isolated products were produced by further reaction. For example, with n-butyllithium and furan in tetrahydrofuran, 108 is produced after hydrogenation and acid treatment via 109. Reaction with phenyllithium gives 110 (R == Ph and Me) by subsequent addition of phenyl or methyl anion to the benzyne, respectively, and 110 (R = I) by subsequent reaction with iodine anion. Similarly the 9,9-diphenyl salt 111 gives 112 with phenyllithium. Pyrolysis of the spiro salt 49 gives 50. 

An efficient and operationally simple synthesis of tetrahydrofuran-derived spiro-P-lactams 15 and 16 using the Staudinger reaction of unsymmetrical cyclic ketones has been described <02JCS(P1)571 02SL69>. Similarly, spiro-P-lactams 17 were synthesized via Staudinger reaction of imines derived from 7-oxanorbomenone with alkoxyacetyl chlorides <02TL6405>. 

Irradiation of 1.00 g (2.98 mmol) of 4,5-dicarbomethoxy-3 -pyrazole-(3-spiro-9)-fluorene in 150 ml of tetrahydrofuran (high-pressure mercury lamp, Hanau Q 81 Pyrex vessel, at 30°C gave a quantitative amount of nitrogen and 0.64 g (70%) of the product. Crystallization from methanol or ether-petroleum ether afforded colorless crystals in 70% yield, mp 146°C. 

The reaction of bicyclo[4.1.0]heptane with diborane and subsequent treatment with hydrogen peroxide produced predominantly cyclohexylmethanol (5b) in high yield.Under modified experimental conditions small amounts of isomeric methylcyclohexanol (6b) and cycloheptanol (7b) were isolated. In contrast to the hydroboration of alkenes, the cyclopropane cleavage reaction is inhibited by ethereal solvents such as diethyl ether, tetrahydrofuran or 2-methoxy-ethyl ether. Bicyclo[3.1.0]hexane reacted with diborane in a similar fashion to give mainly cyclopentylmethanol (5a).The reaction of l-methylbicyclo[4.1.0]heptane gave a mixture of cis- and tram-(2-methylcyclohexyl)methanol (5c) in an initial ratio of 60 40. Spiro[2.5]octane reacted with diborane to yield only products derived from scission at the spiro carbon. The main product was 2-cyclohexylethanol (8). ... 

The spiro-dihydrofuran (61) is converted into the cyclobutane derivative (62) under the influence of trifluoroacetic acid. The lithium dienolate (64), derived from the furanone (63), yields solely y-alkylated products on treatment with alkyl halides. Thermolysis of the t-butylperoxybutenolide (65) produces about equal amounts of the hydroxy-furanone (67) and the indenone (68), presumably via the oxide radical (66). Attack of iodide ion on the salt (69) results in the formation of methyl iodide, butanolide, and (surprisingly) methyl 4-iodobutanoate. A description of a study of the photochemical rearrangement of the tetrahydrofurans (70) to the bicyclic oxetans (71) has been presented. ... 

Segment C (21) is a relatively small molecule and is synthesized from 8. Acyclic stereocontrol for the construction of the C-29 chiral center was very important. Compound 8 was first converted to the lactone (22), which was treated with the carbanion of 23 to give 24. Removal of the sulfone with aluminum amalgam, spiro-ketalization, and Peterson olefination gave 25, which was treated with methyllithium at - 78 °C in tetrahydrofuran. Syn-addition controlled by an a-chelation occurred smoothly to give the expected segment C (21) in high yield [8a, b]. 

Ethylmagnesium bromide magnesium Tetrahydrofuran ring from ketones and 1,3-chlorohydrins Spiro-O-heterocyclics... 

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