Aldehydes from 2-Benzyl-4,4,6-trimethyl-5,6-dihydro, 3 4H -oxazine 1-Phenylcyclopentanecarboxaldehyde

Submitted by Ieva R. Politzer and A. I. Meyers Checked by Dennis R. Rayner and Richard E. Benson 

2- l-Phenylcyclopentyl)-4 , 4, Q-trimethyl-5, Q-dihydro-1, 3(i-H)-oxazine. A 1-1. three-necked flask is equipped with a magnetic stirring bar, a 125-ml. pressure-equalizing funnel fitted with a rubber septum, and a nitrogen inlet tube. The system is flushed with nitrogen and. iOO ml. of dry tctrahydro-furan (Note 1), and 21.7 g. (0.100 mole) of 2-benzyl-4,4,f)- 

4-Dibromobutane (23.8 g., 0.11 mole) (Note 5) is injected into the addition funnel and then is added to the solution with st irring over a period of about 15 minutes. The funnel is rinsed l).y injection of 5 ml. of dry tetrahydrofuran, and the reaction is allowed to stir at —78° for 45 minutes. w-Butyllithium (55 ml., 0.12 mole) in n-hexane is injected into the addition funnel and (hen is added to the solution over a period of 15 minutes. The ritaction is stirred at —78° for 1 hour and then is stored at 

20° overnight (Note 6). The mixture is poured into about 300 ml. of ice water and acidifled to pH 2-3 with 9N hydro-(hloric acid solution. The acidic solution is shaken with three 200-ml. portions of ether, and the ether extracts are discarded. The aqueous layer is made basic by careful addition of 40% sodium hydroxide solution (Note 7). The resulting mixture is shaken with four 200-ml. portions of ether, and the ether extracts are dried over anhydrous potassium carbonate. The eUicr is removed by distillation using a rotaiy evaporator to give 24.4-25.8 g. (90-95%) of crude 2-(l-phenylcyclopentyl)- l,4,6-trimethyl-5,6-dihydro-l,3(4H)-oxazine. The product is sulficiently pure for use in the following step. 

2-(1-Phenylcyclopentyl)-4 , i,Q-trimethyltetrahydro-l,Z-oxa-To a 600-ml. beaker containing a magnetic stirring bar are lidded 200 ml. of tetrahydrofuran, 200 ml. of 95% ethyl alcohol, iMid 25.0 g. (0.092 mole) of the oxazine obtained in Part A. Th( mixture is stirred and cooled to —35 to —40° with an neetone bath to which dry ice is added as needed. A 9N hydrochloric acid solution is added dropwise to the stirred sol lit ion until an approximate pH of 7 is obtained as determined liy )ll paper. A solution of sodium borohydride is prepared by dissolving 5.0 g. (0.13 mole) in a minimum amount of water 

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