35] The MS and MS-MS experiments were carried out on a PE Sciex Qstar Pulsar quadrupole/time-of-flight tandem mass spectrometer (Applied Biosystems, Foster City, California) operated with a room temperature turbo-ionspray source and using Analyst QS data acquisition software. The samples were dissolved in a 1:10 mixture of pyridine and acetonitrile, and infused via a syringe pump at 5 mL min À1 . The instrument was run in the negative ion mode with the capillary voltage at À4500 V and the dissociation potential (source CID) at À20 V. The TOF Pulser frequency was set for 5 kHz with a 1 s accumulation time per spectrum. Data were aquired over the mass range of 10±600 m/z for MS acquisition. In the MS-MS mode, the quadrupole mass analyzer was set to pass the parent ion at unit mass resolution. N 2 or Ar was used as the collision gas. The gas settings were as follows: source nebulizer gas ¼ 30, desolvation gas ¼ 0, curtain gas ¼ 25, collision gas ¼ 5.

Tertiary Grignard reagents and dibromomethane efficiently cyclopropanate allylic (and certain homoallylic) magnesium and lithium alcoholates at ambient temperature in ether solvents. Lithium (homo)allyl alcoholates are directly cyclopropanated with magnesium and CH2Br2 under Barbier conditions at higher temperatures. The reaction rates depend on the substitution pattern of the (homo)allylic alcoholates and on the counterion with lithium giving best results. Good to excellent syn-selectivities are obtained from alpha-substituted substrates, which are in accord with a staggered Houk model. In tandem reactions, cyclopropyl carbinols are obtained from allyloxylithium or -magnesium intermediates, generated in situ by alkylation of conjugated aldehydes, ketones, and esters as well as from allyl carboxylates or vinyloxiranes. Using this methodology, numerous fragrance ingredients and their precursors were efficiently converted to the corresponding cyclopropyl carbinols.

C y c l o p r o p a n a t i o n w i t h D i b r o m o m e t h a n eAbstract: Tertiary Grignard reagents and dibromomethane efficiently cyclopropanate allylic (and certain homoallylic) magnesium and lithium alcoholates at ambient temperature in ether solvents. Lithium (homo)allyl alcoholates are directly cyclopropanated with magnesium and dibromomethane under Barbier conditions at higher temperatures. The reaction rates depend on the substitution pattern of the (homo)allylic alcoholates and on the counterion with lithium giving best results. Good to excellent syn-selectivities are obtained from a-substituted (homo)allyl alcohols. In tandem reactions, cyclopropyl carbinols are obtained from allyloxylithium or -magnesium intermediates, generated in situ by alkylation of conjugated aldehydes, ketones, and esters as well as from allyl esters and carbonates or vinyloxiranes. 1 Scheme 1 OH 1 a OH 2 a (dr = 1:1) CH 2 Br 2 (3 equiv), 10-30 °C, Et 2 O t-BuMgCl (4 equiv), THF, 87% P r o c e d u r e 1 : Deprotonation with t-BuMgCl and cyclopropanation with CH 2 Br 2 P r o c e d u r e 2 : Sequential Grignard addition / cyclopropanation of conjugated aldehydes CHO OH 5 g 2 gPentylMgBr in THF, 0 °C, then CH 2 Br 2 (3 equiv), 10-30 °C, then t-BuMgCl (3 equiv), Et 2 O, 95%

Significance: An efficient cyclopropanation of allylic Mg and Li alcoholates using dibromomethane is described. Reaction rates depend on the substitution pattern of the alcoholates, with a-substituted substrates giving excellent syn selectivity. Furthermore, conjugated aldehydes, ketones and esters have been alkylated using magnesium or lithium reagents yielding intermediate allylic alcoholates which were subsequently cyclopropanated using CH 2 Br 2 .Comment: The authors provide a simple and expeditive cyclopropanation method making use of inexpensive reagents and having relatively positive environmental and safety aspects. This method is of high use in preparative organic chemistry since it can be integrated into the sequential conversion of conjugated aldehydes, ketones, esters or carbonates into cyclopropyl carbinols in high yields and up to 99:1 stereoselectivity. OM R n M = Li, MgX X = Br, Cl R = Alk, alkenyl, Ar n = 2-5 at C α,β,γ α β γ OH R n α β γ t-BuMgCl, CH 2 Br 2 , 0-20 °C or Mg, CH 2 Br 2 , 60 °C in ether solvents S e l e c t e d e x a m p l e s s t a r t i n g f r o m a l l y l i c a l c o h o l s : 95% syn/anti > 99:1 OH 94% syn/anti = 97:3 HO 97% syn/anti > 99:1 OH Sequential Grignard addition to conjugated aldehydes followed by cyclopropanation of the resulting allylic alcoholate (similar procedure for conjugated ketones using alkyllithium reagents) R CHO R n R'MgX ether solvents R R n OMgX R' CH 2 Br 2 (3 equiv) 10-30 °C t-BuMgCl (3 equiv), 20 h OH R n OH Me from the enal and PentMgBr: 95% syn/anti > 99:1 OH from the enal and MeMgCl: 86% syn/anti = 79:21 OH i-Pr from the enone and MeLi: 45% syn/anti > 99:1 E x a m p l e s : SYNFACTS Contributors: