4561-75-5

Upstream product

• 601-57-0 cholest-4-en-3-one 
• 601-57-0 Cholest-4-en-3-one 
• 19493-09-5 Methylenetriphenylphosphorane 
• 75-11-6 diiodomethane 
• 74-95-3 1,1-dibromomethane 
• 1779-49-3 Methyltriphenylphosphonium bromide 

Relevant academic research and scientific papers

An effect of bulk on the ratio of fragmentation to stereomutation in three cyclobutane dimers of 3-methylenecholest-4-ene

The effect of a large increase in mass and extension of substituents on the thermal rearrangement of a 1,2-divinylcyclobutane system has been investigated by the introduction of two 3-cholest-4-ene units. The ratio of two types of exit channel, fragmentation and stereomutation (Fr/St), from a widely accepted diradical intermediary (caldera) has increased significantly relative to the ratio in a simpler system. We believe this to be the first example of the influence of a ponderal effect on the ratio of two competing processes in a thermal rearrangement. The internal torsional rotations necessary prior to reclosure for the realization of stereomutation have been markedly depressed. One of the three stereoisomeric cyclobutanes reacts substantially more slowly than the other two. In its structure, determined by X-ray diffraction, the two cholestenyl wings are folded closely together within van der Waals radii. The slower reaction may reasonably be ascribed to a relative lowering of heat of formation in this ground-state conformation.

A ZIRCONIUM-PROMOTED METHYLENATION OF ALDEHYDES, KETONES, AND ENONES

Treatment of zirconocene dichloride with dibromomethane and zinc affords an organometallic intermediate which rapidly methylenates aldehydes, ketones, and enones at room temperature.

Wittig Reagents Bound to Cross-Linked Polystyrenes

Insoluble benzyltriarylphosphonium and methyltriarylphosphonium salts have been prepared on 2percent and 8percent divinylbenzene cross-linked polystyrene and on 20percent divinylbenzene cross-linked macroporous polystyrene.Phosphoranes were generated with sodium methoxide or sodium ethoxide in THF and with the dimethylsulfinyl carbanion in Me2SO from the benzyl- and methylphosphonium salts, respectively.Reactions of the phosphoranes with a variety of aldehydes and ketones provided alkenes in 73-96percent yields (by GLC analysis) with the 2percent cross-linked polymer, 52-77percent yields with the 8percent cros s-linked polymer, and 72-87percent yields with the 20percent cross-linked macroporous polymer.The rates of phosphorane generation and alkene formation depend on the polymer, decreasing in the order 2percent > 20percent macroporous > 8percent cross-linked.The fraction of E double bond product from the benzylphosphonium salt and either benzaldehyde or cinnamaldehyde is greater with the 20percent cross-linked macroporous polymer than with the 2percent cross-linked polymer.The byproduct polymer-bound phosphine oxides were reduced to phosphines with trichlorsilane, and the phosphines were reused for Wittig synthesis.A quantitative 31P-NMR analysis of phosphine and phosphine oxide residues in polystyrene gels is reported.

Diene Geometry and Allylic Axial Chirality Effect

The sense of the contribution of polarizable allylic axial bonds to the ?-?* Cotton effect of dienes is found to be determined by the chirality of the system which is defined by the direction of the transition moment and direction of the allylic bond.