Chemistry of strained polycyclic compounds—VI : Stereospecific base induced homoketonization of cubane,homocubane and 1,3-bishomocubane bridgehead alcohols

The base induced homoketonization of bridgehead cubane alcohol 10, homocubane alcohol 1 and acetate 7, and 1,3-bishomocubane alcohols 13 and 17 has been studied. Under protic conditions, homocubane alcohol 1 and acetate 7 are converted quantitatively into half cage ketones 3 and 8, respectively, by exclusive cleavage of the C₄C₇ bond. Similarly, homoketonization of 1,3-bishomocubane alcohols 13 and 17 leads to half cage ketones 15 and 18, respectively, by exclusive cleavage of the C₂C₅ bond. As shown by deuterium labeling experiments homoketonization of 1, 7, 13 and 17 proceeds with high stereospecificity and with retention of configuration (96%) at the carbon of substitution. The cubane alcohol 10 gave, under similar conditions, complex mixtures of ring-opened products. Under aprotic conditions, base treatment of homocubane alcohol 1 leads to cleavage of the C₃C₄ and C₂C₅ bond giving the tricyclo[4.2.1.0.^2,5]nonene 21. The mechanism of homoketonization is discussed.     

Synthesis of α,β-epoxy diazomethyl ketones

The preparation of eighteen epoxy diazomethyl ketones 1 is described. Two general methods were developed. Firstly, treatment of the mixed anhydrides of glycidic acids and carbonic acid ester with diazomethane led to the title compounds in yields ranging from 17–74%. Secondly, glycidyl chlorides which were obtained from sodium glycidates and oxalyl chloride, gave the desired products upon treatment with diazomethane (yields 60–74%). The required α,β-epoxy carboxylic esters were prepared by Darzens condensation and epoxidation of α,β-unsaturated esters, but in some cases also by reaction of α-oxo carboxylic esters with diazomethane.     

Facial Selectivity in the Nucleophilic Additions of endo-Tricyclo[5.2.1.0~(2,6)]deca-2(6),8-dien-3-one

The endo-tricyclo [5.2.1.02,6] decadienone system 1 has been used as a versatile synthon for the synthesis of a great variety of natural products1. The availability of both antipodes of 1 in enantiopure form2, and the ability to undergo [4+2] cycloreversion makes it useful for the enantioselective synthesis of naturally occurring cyclopentanoids with defined stereochemistry and chirality3. Starting from the 1,4 reduced Hertz ester 2, synthesis of the reactive and strained tricyclodecadienone 4…     

Crystal and molecular structure of (2E,4S,10R)-4-hydroxy-2-undecen-10-olide (nor-patulolide C), C11H18O3

The stereogeometry and absolute configuration of the title compound has been proved by an X-ray diffraction analysis. Crystal data: monoclinic, P2₁,a=7.7976(2),b=7.8288(2),c=8.9791(4) Å, =90.331(4)^o, Z=2. The crystal structure has been solved by vector search methods and refined toR=0.042 for 1798 observed reflections.     

Enantio-controlled synthesis of the crocyclic C14-C23 subunit of cytochalasin b

The synthesis of the C₁₄-C₂₃ macrocyclic subunit of cytochalasin B from pulegone is described. The key feature of this synthesis is the photo-induced rearrangement of epoxy diazomethyl ketone E to a γ-hydroxy alkenoic ester (Scheme 2). The intermediate epoxy alcohol F was prepared using the asymmetric Sharpless epoxidation. Considerable attention was given to the preparation of allylic alcohol 14, having a t-butyldimethylsilyloxy protecting function, as starting material for the asymmetric epoxidation, however, several unforeseen difficulties were encountered (Schemes 3 and 4). Satisfactory results were obtained using the methoxy group as protecting function (Scheme 5). The allylic alcohol 22 was prepared from bromide 20 by chain lengthening with propargyl alcohol. The Sharpless epoxidation of 22 took place with high induction. Conversion to epoxy ester 24, to diazo ketone 25 and photo-rearrangement to 26 and deprotection to give 28, completes the sequence.     

Reactions of diazomethane with sulfonyl-activated double bonds

The cyclo-addition reaction of diazomethane with α,β-unsaturated sulfones is described. Divinyl sulfone and phenyl vinyl sulfone give 1- or 2-pyrazolines depending on the reaction conditions. cis- and trans-1,2-Bis(methylsulfonyl)ethene form pyrazolines, which on reaction with either triethylamine or excess of diazomethane lead to substituted pyrazoles.     

Computational analysis of the nucleophilic eliminative ring fission of bridgehead substituted 1,3-bishomocubyl acetates

Molecular mechanics (MM2) calculations on the conceivable seco-cage structures by homoketonization of two types of bridgehead substituted 1,3-bishomocubyl acetates, viz. type A : 4-acetoxy-pentacyclo[5.3.0.0^2,5.0^3,9.0^4,8] decan-6-one and its ethylene ketal, and type B: 8-acetoxypentacyclo [5.3.0.0^2,5.0^3,9.0^4,8]decan-6-one, its ethylene ketal and 8-acetoxypentacyclo[5.3.0.0^2,5.0^3,9.0^4,8]decane were performed.